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

                                  SCHEDULE 13D
                                 (Rule 13d-101)

                                (Amendment No. 3)

    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

                                125 Broad Street
                            New York, New York 10004
                                 (212) 558-4000

                                December 21, 2001
     ----------------------------------------------------------------------
             (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 7 Pages)

--------------------                                           -----------------
CUSIP NO. 74158J103                                            PAGE 2 OF 7 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 ITEMS 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                          7,944,893
    EACH                   -----------------------------------------------------
 REPORTING                 9.       SOLE DISPOSITIVE POWER
   PERSON                           0
    WITH                   -----------------------------------------------------
                           10.      SHARED DISPOSITIVE POWER
                                    7,944,893

--------------------------------------------------------------------------------
11.      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         7,944,893

--------------------------------------------------------------------------------
12.      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
         CERTAIN SHARES                     [  ]
--------------------------------------------------------------------------------
13.      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
         33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.      TYPE OF REPORTING PERSON
         OO (real estate investment trust)


                                       -2-

--------------------                                           -----------------
CUSIP NO. 74158J103                                            PAGE 3 OF 7 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 ITEMS 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                          7,944,893
    EACH                   -----------------------------------------------------
 REPORTING                 9.       SOLE DISPOSITIVE POWER
   PERSON                           0
    WITH                   -----------------------------------------------------
                           10.      SHARED DISPOSITIVE POWER
                                    7,944,893

--------------------------------------------------------------------------------
11.      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         7,944,893

--------------------------------------------------------------------------------
12.      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
         CERTAIN SHARES                                                [  ]
--------------------------------------------------------------------------------
13.      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
         33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.      TYPE OF REPORTING PERSON
         PN


                                       -3-

--------------------                                          -----------------
CUSIP NO. 74158J103                                           PAGE 4 OF 7 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 ITEMS 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                          7,944,893
    EACH                   -----------------------------------------------------
 REPORTING                 9.       SOLE DISPOSITIVE POWER
   PERSON                           0
    WITH                   -----------------------------------------------------
                           10.      SHARED DISPOSITIVE POWER
                                    7,944,893
--------------------------------------------------------------------------------
11.      AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         7,944,893

--------------------------------------------------------------------------------
12.      CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES
         CERTAIN SHARES                     [  ]
--------------------------------------------------------------------------------
13.      PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
         33.6% as calculated in accordance with Rule 13d-3(d)(1)
--------------------------------------------------------------------------------
14.      TYPE OF REPORTING PERSON
         OO (limited liability company)


                                       -4-

                         AMENDMENT NO. 3 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. 3 to Schedule 13D ("Amendment No. 3") 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 and by
Amendment No. 2 to Schedule 13D of the Reporting Persons filed on December 19,
2001 (as so amended, the "Schedule 13D"). This Amendment No. 3 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 paragraph at the end thereof:

         On December 21, 2001, Vornado PS and the Operating Partnership
delivered to the Issuer's Board letters from Michael W. Reschke and Richard S.
Curto resigning from the Board of Trustees of the Issuer and each similar
governing body of each entity controlled by the Issuer and from each office held
by them with the Issuer and each entity controlled by the Issuer. These
resignation letters had previously been delivered to, and held in escrow by, the
Operating Partnership pursuant to the terms of the documentation relating to the
Subordinated Loan, and the Operating Partnership became entitled to deliver
these letters upon commencement of the Borrower's bankruptcy proceedings that
have been previously reported. As previously reported, on November 14, 2001, Mr.
Reschke and various affiliated entities filed a Schedule 13D amendment in which
they claimed that he and Mr. Curto have rescinded these resignations. As also
previously reported, the Reporting Persons do not believe that Messrs. Reschke
and Curto have the power to revoke these resignations, and do not believe that
these purported rescissions were effective.

                                      -5-


For more information concerning such letters of resignation, see Item 6.

Item 5.  Interest in Securities of the Issuer.

Item 5 is hereby amended by adding the following sentence at the end of
paragraph (c) thereof:

         No transactions in the Common Shares were effected by Reporting Persons
since December 19, 2001, except to the extent that such transactions may be
deemed to have occurred as described in Item 4.


                                       -6-

                                   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: December 21, 2001

                                        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 Officer


                                       -7-