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

                                  SCHEDULE 13D
                                 (Rule 13d-101)

                                (Amendment No. 12)

    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

                                 April 30, 2002
         --------------------------------------------------------------
             (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. 12 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. 12 to Schedule 13D ("Amendment No. 12") 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 and by
Amendment No. 11 to Schedule 13D of the Reporting Persons filed on April 19,
2002 (as so amended, the "Schedule 13D"). This Amendment No. 12 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 two paragraphs at the end
thereof:

         On April 30, 2002, Vornado PS acquired 7,944,893 Common Units in Prime
Group Realty, L.P. at the Foreclosure Auction held in New York City. The price
Vornado PS paid for the Common Units was $8.35 per unit, which was paid by
application of a portion of the Borrower's indebtedness to Vornado PS. That
price equaled the April 30, 2002 closing price on the New York Stock Exchange of
the Issuer's Common Shares for which the Common Units are exchangeable on a
one-for-one basis. The Borrower and certain of its affiliates remain liable for
the deficiency under the Loans.

         As previously reported, Cadim Acquisition owns a 50% participation
interest in the Loans to the Borrower held by Vornado PS.


                                      -5-



         As a result of Vornado PS's acquisition of the Common Units at the
Foreclosure Auction, Cadim Acquisition now owns a 50% participation interest in
these Common Units as well as a 50% participation interest in the remainder of
the Loans. Under the Participation Agreement, Vornado PS and the Operating
Partnership, on the one hand, and Cadim Acquisition and Cadim inc, on the other
hand, have various rights and obligations with respect to the Common Units that
were acquired in the Foreclosure Auction (as well as the Common Shares for which
they may be exchanged), the Loans and the parties' relationship with the Issuer.
Those rights and obligations are set forth in the Participation Agreement which
has been filed as Exhibit 99.12 to this Schedule 13D and which is expressly
incorporated herein by reference.

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 April 19, 2002, 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: May 1, 2002

                                  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-