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

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                               (AMENDMENT NO. 3 )*

                           Iron Mountain Incorporated
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                                (Name of Issuer)

                                  Common Stock
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                         (Title of Class of Securities)

                                   462846 10 6
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                                 (CUSIP Number)

                                December 31, 2003
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             (Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

         [X] Rule 13d-1(b)

         [ ] Rule 13d-1(c)

         [ ] Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a cover page.

The information required in 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 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).



CUSIP No.     462846 10 6

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     1.   Names of Reporting Persons.
          I.R.S. Nos. of above persons (entities only).

                      Chieftain Capital Management, Inc.   13-3194313
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     2.   Check the Appropriate Box if a Member of a Group (See Instructions)

          a.   Not Applicable

          b.   Not Applicable

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     3.   SEC Use Only

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     4.   Citizenship or Place of Organization New York

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Number of                  5.  Sole Voting Power            -0-
Shares Bene-
ficially Owned             6.  Shared Voting Power       11,228,800
By Each
Reporting                  7.  Sole Dispositive Power       -0-
Person With:
                           8.  Shared Dispositive Power  11,228,800

     9.   Aggregate Amount Beneficially Owned by Each Reporting Person
          11,228,800

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     10.  Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See
Instructions) Not Applicable

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     11.  Percent of Class Represented by Amount in Row (9) 13.2%

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     12.  Type of Reporting Persons (See Instructions)
                          IA, CO
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ITEM 1.

     (a)  Name of Issuer: Iron Mountain Incorporated

     (b)  Address of Issuer's Principal Executive Offices:

                           745 Atlantic Avenue
                           Boston, Massachusetts 02111

ITEM 2.

     (a)  Name of Person Filing: Chieftain Capital Management, Inc.

     (b)  Address of Principal Business Office or, if none, Residence:

                           12 East 49th Street
                           New York, New York 10017

     (c)  Citizenship: New York

     (d)  Title of Class of Securities: Common Stock

     (e)  CUSIP Number: 462846 10 6

ITEM 3.   IF THIS STATEMENT IS FILED PURSUANT TO SECTIONS 240.13d-1(b)
          OR 240.13d-2(b) OR (c), CHECK WHETHER THE PERSON FILING IS A:

     (a)  [ ] Broker or dealer registered under Section 15 of the Act (15 U.S.C.
          78o);

     (b)  [ ] Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);

     (c)  [ ] Insurance company as defined in section 3(a)(19) of the Act (15
          U.S.C. 78c);

     (d)  [ ] Investment company registered under section 8 of the Investment
          Company Act of 1940 (15 U.S.C. 80a-8);

     (e)  [X] An investment advisor in accordance with Section
          240.13d-1(b)(1)(ii)(E);

     (f)  [ ] An employee benefit plan or endowment fund in accordance with
          Section 240.13d-1(b)(1)(ii)(F);

     (g)  [ ] A parent holding company or control person in accordance with
          Section 240.13d-1(b)(ii)(G);

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     (h)  [ ] A savings association as defined in Section 3(b) of the Federal
          Deposit Insurance Act (12 U.S.C. 1813);

     (i)  [ ] A church plan that is excluded from the definition of an
          investment company under section 3(c)(14) of the Investment Company
          Act of 1940 (15 U.S.C. 80a-3);

     (j)  [ ] Group, in accordance with Section 240.13d-1(b)(1)(ii)(J).

ITEM 4.   Ownership

     (a)  Amount beneficially owned: 11,228,800

     (b)  Percent of class: 13.2%

     (c)  Number of shares as to which the person has:

          (i)   Sole power to vote or to direct the vote: -0-

          (ii)  Shared power to vote or to direct the vote: 11,228,800

          (iii) Sole power to dispose or to direct the disposition of: -0-

          (iv)  Shared power to dispose or to direct the disposition of:
                11,228,800

ITEM 5.   OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

          If this statement is being filed to report the fact that as of the
          date hereof the reporting person has ceased to be the beneficial owner
          of more than five percent of the class of securities, check the
          following [ ].

ITEM 6.   OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

          Chieftain Capital Management, Inc. ("Chieftain") has investment
          discretion with respect to the securities to which this statement
          relates. Chieftain's clients and principals are the direct owners of
          such securities, and Chieftain does not have any economic interest in
          such securities. Such clients and principals have the sole right to
          receive dividends from, and the proceeds from the sale of, such
          securities. No such client or principal has an interest that relates
          to more than 5% of the class.

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ITEM 7.   IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
          SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

                                 Not Applicable

ITEM 8.   IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

                                 Not Applicable

ITEM 9.   NOTICE OF DISSOLUTION OF GROUP

                                 Not Applicable

ITEM 10.  CERTIFICATION

          By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired and are held in the
ordinary course of business and were not acquired and are not held for the
purpose of or with the effect of changing or influencing the control of the
issuer of the securities and were not acquired and are not held in connection
with or as a participant in any transaction having that purpose or effect.

                                    SIGNATURE

          After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

                                February 12, 2004
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                                      Date

                               /s/ Thomas D. Stern
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                                    Signature

                        Thomas D. Stern/Managing Director
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                                   Name/Title

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