UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13D
                                 (Rule 13d-101)

                               (Amendment No. 19)

    INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(a)
                    AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13d-2(a)

                            Prime Group Realty Trust
- --------------------------------------------------------------------------------
                                (Name of Issuer)

                      Common Shares of Beneficial Interest,
                            par value $0.01 per share
                            -------------------------
                         (Title of Class of Securities)

                                    74158J103
                                    ---------
                                 (CUSIP Number)

                                  Joseph Macnow
                              Vornado Realty Trust
                               888 Seventh Avenue
                            New York, New York 10019
                                 (212) 894-7000
- --------------------------------------------------------------------------------
            (Name, Address and Telephone Number of Person Authorized
                     to Receive Notices and Communications)

                                 With a copy to:
                                William G. Farrar
                                 Alan Sinsheimer
                             Sullivan & Cromwell LLP
                                125 Broad Street
                            New York, New York 10004
                                 (212) 558-4000

                                  July 5, 2003
             -------------------------------------------------------
             (Date of Event Which Requires Filing of This Statement)

If a filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box
[ ].

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities
of that section of the Exchange Act but shall be subject to all other provisions
of the Exchange Act.

                         (Continued on following pages)

                               (Page 1 of 8 Pages)


- -------------------- --------------------- CUSIP NO. 74158J103 PAGE 2 OF 8 PAGES - -------------------- --------------------- - -------------------------------------------------------------------------------- 1. NAME OF REPORTING PERSON: Vornado Realty Trust I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY): 22-1657560 - -------------------------------------------------------------------------------- 2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [X] (b) [ ] - -------------------------------------------------------------------------------- 3. SEC USE ONLY - -------------------------------------------------------------------------------- 4. SOURCE OF FUNDS: AF - -------------------------------------------------------------------------------- 5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e) [ ] - -------------------------------------------------------------------------------- 6. CITIZENSHIP OR PLACE OF ORGANIZATION Maryland - -------------------------------------------------------------------------------- 7. SOLE VOTING POWER NUMBER OF 0 SHARES ----------------------------------------------------------------- BENEFICIALLY 8. SHARED VOTING POWER OWNED BY 3,972,447 EACH ----------------------------------------------------------------- REPORTING 9. SOLE DISPOSITIVE POWER PERSON 0 WITH ----------------------------------------------------------------- 10. SHARED DISPOSITIVE POWER 3,972,447 - -------------------------------------------------------------------------------- 11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,972,447 - -------------------------------------------------------------------------------- 12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES [X] - -------------------------------------------------------------------------------- 13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 16.8% as calculated in accordance with Rule 13d-3(d)(1) - -------------------------------------------------------------------------------- 14. TYPE OF REPORTING PERSON OO (real estate investment trust) -2 of 8-

- -------------------- --------------------- CUSIP NO. 74158J103 PAGE 3 OF 8 PAGES - -------------------- --------------------- - -------------------------------------------------------------------------------- 1. NAME OF REPORTING PERSON: Vornado Realty L.P. I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY): 13-3925979 - -------------------------------------------------------------------------------- 2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [X] (b) [ ] - -------------------------------------------------------------------------------- 3. SEC USE ONLY - -------------------------------------------------------------------------------- 4. SOURCE OF FUNDS WC - -------------------------------------------------------------------------------- 5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e) [ ] - -------------------------------------------------------------------------------- 6. CITIZENSHIP OR PLACE OF ORGANIZATION Delaware - -------------------------------------------------------------------------------- 7. SOLE VOTING POWER NUMBER OF 0 SHARES ----------------------------------------------------------------- BENEFICIALLY 8. SHARED VOTING POWER OWNED BY 3,972,447 EACH ----------------------------------------------------------------- REPORTING 9. SOLE DISPOSITIVE POWER PERSON 0 WITH ----------------------------------------------------------------- 10. SHARED DISPOSITIVE POWER 3,972,447 - -------------------------------------------------------------------------------- 11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,972,447 - -------------------------------------------------------------------------------- 12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES [X] - -------------------------------------------------------------------------------- 13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 16.8% as calculated in accordance with Rule 13d-3(d)(1) - -------------------------------------------------------------------------------- 14. TYPE OF REPORTING PERSON PN -3 of 8-

- -------------------- --------------------- CUSIP NO. 74158J103 PAGE 4 OF 8 PAGES - -------------------- --------------------- - -------------------------------------------------------------------------------- 1. NAME OF REPORTING PERSON: Vornado PS, L.L.C. I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY): - -------------------------------------------------------------------------------- 2. CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) [X] (b) [ ] - -------------------------------------------------------------------------------- 3. SEC USE ONLY - -------------------------------------------------------------------------------- 4. SOURCE OF FUNDS: AF - -------------------------------------------------------------------------------- 5. CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e) [ ] - -------------------------------------------------------------------------------- 6. CITIZENSHIP OR PLACE OF ORGANIZATION Delaware - -------------------------------------------------------------------------------- 7. SOLE VOTING POWER NUMBER OF 0 SHARES ----------------------------------------------------------------- BENEFICIALLY 8. SHARED VOTING POWER OWNED BY 3,972,447 EACH ----------------------------------------------------------------- REPORTING 9. SOLE DISPOSITIVE POWER PERSON 0 WITH ----------------------------------------------------------------- 10. SHARED DISPOSITIVE POWER 3,972,447 - -------------------------------------------------------------------------------- 11. AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 3,972,447 - -------------------------------------------------------------------------------- 12. CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES [X] - -------------------------------------------------------------------------------- 13. PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11) 16.8% as calculated in accordance with Rule 13d-3(d)(1) - -------------------------------------------------------------------------------- 14. TYPE OF REPORTING PERSON OO (limited liability company) -4 of 8-

AMENDMENT NO. 19 TO SCHEDULE 13D RELATING TO THE COMMON SHARES OF BENEFICIAL INTEREST OF PRIME GROUP REALTY TRUST Vornado Realty Trust ("Vornado"), Vornado Realty L.P. (the "Operating Partnership") and Vornado PS, L.L.C. ("Vornado PS" and, collectively with Vornado and the Operating Partnership, the "Reporting Persons") hereby amend their Statement on Schedule 13D filed with respect to the Common Shares of Beneficial Interest, par value $0.01 per share ("Common Shares"), of Prime Group Realty Trust, a Maryland real estate investment trust (the "Issuer"). This Amendment No. 19 to Schedule 13D ("Amendment No. 19") should be read in conjunction with the Statement on Schedule 13D of the Reporting Persons filed on November 2, 2001 (the "Initial Schedule 13D"), as amended by Amendment No. 1 to Schedule 13D of the Reporting Persons filed on November 20, 2001, by Amendment No. 2 to Schedule 13D of the Reporting Persons filed on December 19, 2001, by Amendment No. 3 to Schedule 13D of the Reporting Persons filed on December 21, 2001, by Amendment No. 4 to Schedule 13D of the Reporting Persons filed on December 27, 2001, by Amendment No. 5 to Schedule 13D of the Reporting Persons filed on January 15, 2002, by Amendment No. 6 to Schedule 13D of the Reporting Persons filed on January 31, 2002, by Amendment No. 7 to Schedule 13D of the Reporting Persons filed on February 7, 2002, by Amendment No. 8 to Schedule 13D of the Reporting Persons filed on February 20, 2002, by Amendment No. 9 to Schedule 13D of the Reporting Persons filed on March 29, 2002, by Amendment No. 10 to Schedule 13D of the Reporting Persons filed on April 17, 2002, by Amendment No. 11 to Schedule 13D of the Reporting Persons filed on April 19, 2002, by Amendment No. 12 to Schedule 13D of the Reporting Persons filed on May 1, 2002, by Amendment No. 13 to Schedule 13D of the Reporting Persons filed on May 14, 2002, by Amendment No. 14 to Schedule 13D of the Reporting Persons filed on July 3, 2002, by Amendment No. 15 to Schedule 13D of the Reporting Persons filed on December 23, 2002, by Amendment No. 16 to Schedule 13D of the Reporting Persons filed on May 27, 2003, by Amendment No. 17 to Schedule 13D of the Reporting Persons filed on June 13, 2003, and by Amendment No. 18 to Schedule 13D of the Reporting Persons filed on June 18, 2003 (as so amended, the "Schedule 13D"). This Amendment No. 19 amends the Schedule 13D only with respect to the items listed below. Unless otherwise indicated, all capitalized terms used but not defined herein shall have the meaning ascribed to them in the Initial Schedule 13D. Pursuant to Rule 13d-4 under the Exchange Act, each of the Reporting Persons declares that the filing of this statement shall not be construed as an admission that such Reporting Person is, for the purposes of Section 13(d) or 13(g) of the Exchange Act, the beneficial owner of any Common Shares. Any disclosures made herein with respect to persons other than the Reporting Persons are made on information and belief after making appropriate inquiry. Item 4. Purpose of the Transaction. Item 4 is hereby amended by adding the following paragraphs at the end thereof: Pursuant to the terms of the November 19, 2001 Participation Agreement among Vornado PS and the Operating Partnership, on the one hand, and Cadim inc. ("Cadim") and Cadim Acquisition, LLC ("Cadim Acquisition" and together with -5 of 8-

Cadim, the "Cadim Parties"), on the other hand, the consent rights that the Reporting Persons had with respect to the sale or other disposition of Common Shares held by the Cadim Parties and that the Cadim Parties had with respect to the sale or other disposition of Common Shares held by the Reporting Persons, terminated on July 5, 2003. In addition, on July 5, 2003, also pursuant to the terms of the Participation Agreement, the consent rights of the Reporting Persons with respect to the solicitation or making of any proposal or offer with respect to a merger, acquisition or other business combination involving the Issuer by the Cadim Parties and the consent rights of the Cadim Parties with respect to the solicitation or making of any proposal or offer with respect to a merger, acquisition or other business combination involving the Issuer by the Vornado Parties, terminated. As previously disclosed, each of the Vornado Parties will continue to assess its position relative to the Issuer and, depending on market conditions, the Issuer's financial condition, business, operations and prospects and other factors, may: acquire Common Units, other Common Shares or debt or equity securities of the Issuer or its subsidiaries, in the open market, in private transactions or otherwise; seek representation on or control of the board of directors of the Issuer; dispose of all or any portion of the Common Shares or other securities it may hereafter acquire; seek to engage, by itself or with one or more additional parties, which may or may not include the Cadim Parties, in one or more extraordinary transactions, such as tender offers, mergers, reorganizations or liquidations involving the Issuer or any of its subsidiaries or purchases or sales of a material amount of the assets of the Issuer or any of its subsidiaries; engage in discussions with the management and/or significant shareholders of the Issuer, or otherwise make a plan or proposal, with respect to any of the foregoing; and/or take any other action which it may deem to be appropriate in the circumstances. It is possible that any of the Vornado Parties, with or without any of the Cadim Parties, may from time to time formulate preliminary plans or proposals with respect to a possible strategic transaction relating to the Issuer or the Common Shares. The Reporting Persons do not expect to amend this Amendment No. 19 with respect to any plans or proposals relating to any of the foregoing until such time (if ever) as those plans or proposals become definitive enough to warrant disclosure. As of the date hereof, the Vornado Parties believe, based upon information contained in the Schedule 13D filed on July 23, 2003 by the Cadim Parties, that the Cadim Parties have beneficial ownership of 3,972,446 Common Shares, representing 16.8% of the outstanding Common Shares. Item 5. Interest in Securities of the Issuer. Item 5(a) is hereby amended to read in its entirety as follows: See Items 11 and 13 on each of pages 2, 3, and 4 above, which items are incorporated herein by reference. By reason of the termination of the consent and other rights described in Item 4 of this Schedule 13D, the Reporting Persons believe they no longer may be deemed to constitute a group for purposes of Section 13(d) or 13(g) of the Exchange Act with the Cadim Parties. The filing of this Schedule 13D shall not be construed as an admission that any of the Reporting Persons was at any time the beneficial owner for purposes of Section 13(d) or 13(g) of the Exchange Act of any securities held by any other person. Item 5(b) is hereby amended to read in its entirety as follows: -6 of 8-

See Items 7,8,9, and 10 on each of pages 2, 3, and 4 above, which items are incorporated herein by reference. By reason of the termination of the consent and other rights described in Item 4 of this Schedule 13D, the Reporting Persons believe they no longer may be deemed to constitute a group for purposes of Section 13(d) or 13(g) of the Exchange Act with the Cadim Parties. The filing of this Schedule 13D shall not be construed as an admission that any of the Reporting Persons was at any time the beneficial owner for purposes of Section 13(d) or 13(g) of the Exchange Act of any securities held by any other person. Item 5(c) is hereby amended by adding the following sentence at the end thereof: No transactions in the Common Shares were effected by the Reporting Persons since June 18, 2003, the date of execution of the Reporting Persons' most recent filing, except to the extent that such transactions may be deemed to have occurred as described in Item 4 and 6. Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer. Item 6 is hereby amended by adding the following paragraph at the end thereof: As disclosed in the Initial Schedule 13D, pursuant to the terms and conditions of the Registration Rights Agreement, dated as of November 17, 1997 (the "Registration Rights Agreement"), by and among the Issuer and the other parties thereto, the Issuer granted certain demand and incidental registration rights to certain holders of Common Units for the registration under the Securities Act of 1933, as amended, of Common Shares issuable upon exchange of such Common Units. As a result of their acquisition of Common Shares, Vornado PS and Cadim Acquisition now share certain rights under the Registration Rights Agreement. On July 22, 2003, the Operating Partnership and Vornado PS, on the one hand, and the Cadim Parties, on the other, agreed that neither Vornado PS nor Cadim Acquisition shall have the right to cause more than one registration per calendar year pursuant to Section 3.1 of the Registration Rights Agreement, without the consent of the other parties. As of the date hereof, the Vornado Parties believe, based upon information contained in the Schedule 13D filed by the Cadim Parties on July 23, 2003, that the Cadim Parties have beneficial ownership of 3,972,446 Common Shares that may be covered by the Registration Rights Agreement. For information with respect to Item 6 matters covered in the Registration Rights Agreement, see Exhibit 99.10 and 99.13 to this Schedule 13D. The information set forth in response to this item is qualified in its entirety by reference to the documents which are filed as Exhibits 99.10 and 99.13 to this Schedule 13D. Item 7. Material to Be Filed as Exhibits. 99.13 Agreement, dated July 22, 2003, among Vornado Realty L.P., Vornado PS, L.L.C., Cadim Acquisition, LLC and Cadim, inc. -7 of 8-

SIGNATURES After reasonable inquiry and to the best of my knowledge and belief, each of the undersigned certifies that the information set forth in this amendment to Schedule 13D is true, complete and correct. Dated: July 29, 2003 VORNADO REALTY TRUST By: /s/ Joseph Macnow --------------------------------- Name: Joseph Macnow Title: Executive Vice President-Finance and Administration, Chief Financial Officer VORNADO REALTY L.P. By: VORNADO REALTY TRUST, its general partner By: /s/ Joseph Macnow --------------------------------- Name: Joseph Macnow Title: Executive Vice President-Finance and Administration, Chief Financial Officer VORNADO PS, L.L.C. By: VORNADO REALTY L.P., its sole member By: VORNADO REALTY TRUST, its general partner By: /s/ Joseph Macnow --------------------------------- Name: Joseph Macnow Title: Executive Vice President-Finance and Administration, Chief Financial -8 of 8-





                                                        July 22, 2003




Cadim Acquisition, LLC
c/o Cadim inc.
Centre CDP Capital
1000, place Jean-Paul Riopelle
Bureau A-300
Montreal, Quebec H22 2B6
Attention:    Richard Dansereau
Facsimile:    (514) 875-3327

Cadim inc.
Centre CDP Capital
1000, place Jean-Paul Riopelle
Bureau A-300
Montreal, Quebec H22 2B6
Attention:    Richard Dansereau
Facsimile:    (514) 875-3327

         Re:  Purchase and Sale of Loan Participation among Vornado PS, L.L.C.,
              a Delaware limited liability company (the "Lender"), Vornado
              Realty L.P. ("VRLP"), a Delaware limited partnership, Cadim
              Acquisition, LLC, a Delaware limited liability company (the
              "Participant"), and Cadim inc., a company incorporated under the
              laws of Quebec ("Cadim").
              ------------------------------------------------------------------

Gentlemen/Ladies:

         Reference is made to that certain agreement, dated November 19, 2001
(the "Participation Agreement"), by and among Lender, VRLP, Participant and
Cadim. Reference is also made to that certain Registration Rights Agreement,
dated as of November 17, 1997 (the "Registration Rights Agreement"), among Prime
Group Realty Trust, Prime Group Realty, L.P., Prime Group Limited Partnership,
Primestone Investment Partners L.P. and the other investors named therein.


Cadim Acquisition, LLC -2- Cadim inc. The parties hereto hereby agree that (i) the Exclusivity Period Termination Date (as defined in Section 5(b) of the Participation Agreement) has occurred and (ii) Section 5(b) of the Participation Agreement shall be of no further force or effect, including, without limitation, any rights of first offer described therein. The parties hereto also hereby agree that each of Lender and its successors and assigns, on the one hand, and Participant and its successors and assigns, on the other hand, shall have the right to cause not more than one registration of Eligible Securities (as defined in the Registration Rights Agreement) under Section 3.1 of the Registration Rights Agreement in any calendar year without the prior written consent of the other party hereto. THIS AGREEMENT SHALL BE CONSTRUED AND ENFORCEABLE IN ACCORDANCE WITH, AND GOVERNED BY, THE LAWS OF THE STATE OF NEW YORK. Wherever possible, each provision of this agreement shall be interpreted in such manner as to be effective and valid under applicable law, but if any provision of this agreement shall be prohibited by or invalid under applicable law, such provision shall be ineffective to the extent of such prohibition or invalidity, without invalidating the remainder of such provision or the remaining provisions of this agreement. This agreement may be executed in any number of counterparts, each of which when so executed and delivered shall be an original, but all of which shall constitute one and the same instrument. It shall not be necessary in making proof of this agreement to produce or account for more than one copy of such instrument. Each of the parties hereto irrevocably agrees that any legal action or proceeding against it arising out of or in connection with this agreement or for recognition or enforcement of any judgment rendered in any such action or proceeding may be brought in the United States Courts or the State of New York Courts, in each case located in the Borough of Manhattan, City and State of New York, and by execution and delivery of this agreement, each party hereby irrevocably accepts and submits to the jurisdiction of each of the aforesaid courts in personam, generally and unconditionally with respect to any such action or proceeding. Each of the parties hereto further irrevocably consents to the service of process out of said courts by mailing a copy thereof, by registered or certified mail, postage prepaid to it at the address set forth for such party herein below. Each of the parties hereto also irrevocably waives, to the fullest extent permitted by law, any objection which it may now or hereafter have to the laying of venue of any such action or proceeding brought in any such court and any claim that any such action or proceeding brought in such court has been brought in an inconvenient forum. Each of the parties hereto irrevocably agrees that, should either party institute any

Cadim Acquisition, LLC -3- Cadim inc. legal action or proceeding in any jurisdiction (whether for an injunction, specific performance, damages or otherwise) in relation to this agreement, no immunity (to the extent that it may at any time exist, whether on the grounds of sovereignty or otherwise) from such action or proceeding shall be claimed by it or on its behalf, any such immunity being hereby irrevocably waived and that each of the parties hereto each irrevocably agrees that it and its assets are, and shall be, subject to such legal action or proceeding in respect of its obligations under this agreement. Each of the parties hereto hereby waives any right to trial by jury in connection with any action, proceeding or counterclaim instituted with respect to this agreement. [Signature Page Follows]

Cadim Acquisition, LLC -4- Cadim inc. Please indicate the Participant's and Cadim's agreement to the foregoing by executing this agreement on the line provided below and returning to the undersigned two copies of this agreement. VORNADO PS, L.L.C., a Delaware limited liability company By: Vornado Realty L.P., a Delaware limited partnership and its Sole Member By: Vornado Realty Trust, a Maryland real estate investment trust and its General Partner By: /s/ Michael D. Fascitelli -------------------------------- Name: Michael D. Fascitelli Title: President Address: Vornado PS, L.L.C. 888 Seventh Avenue, 44th Floor New York, New York 10019 Attention: Michael Fascitelli Facsimile: (212) 894-7070 Telephone: (212) 894-7000 Attention: Joseph Macnow Facsimile: (201) 587-1388 Telephone: (201) 587-1000

Cadim Acquisition, LLC -5- Cadim inc. VORNADO REALTY L.P., a Delaware limited partnership By: Vornado Realty Trust, a Maryland real estate investment trust and its General Partner By: /s/ Michael D. Fascitelli -------------------------------- Name: Michael D. Fascitelli Title: President Address: Vornado Realty L.P. 888 Seventh Avenue, 44th Floor New York, New York 10019 Attention: Michael Fascitelli Facsimile: (212) 894-7070 Telephone: (212) 894-7000 Attention: Joseph Macnow Facsimile: (201) 587-1388 Telephone: (201) 587-1000

Cadim Acquisition, LLC -2- Cadim inc. Accepted and Agreed to: CADIM ACQUISITION, LLC, a Delaware limited liability company By: Cadim Holdings U.S. Inc., a Delaware corporation, its sole member By: /s/ Sylvia Drouin ------------------------------------- Name: Sylvia Drouin Title: Secretary By: /s/ Line Lefevbre ------------------------------------- Name: Line Lefevbre Title: Treasurer Address: c/o Cadim inc. Centre CDP Capital 1000, place Jean-Paul Riopelle Bureau A-300 Montreal, Quebec H22 2B6 Attention: Richard Dansereau Facsimile: (514) 875-3327 Telephone: (514) 875-3360 CADIM INC., a company incorporated under the laws of Quebec By: /s/ Sylvia Drouin ------------------------------------- Name: Sylvia Drouin Title: Vice-President, Legal Affairs By: /s/ Line Lefevbre ------------------------------------- Name: Line Lefevbre Title: Senior Vice President, Finance and Administration Address: Centre CDP Capital 1000, place Jean-Paul Riopelle Bureau A-300 Montreal, Quebec H22 2B6 Attention: Richard Dansereau Facsimile: (514) 875-3327 Telephone: (514) 875-3360