<PAGE>


                                                                    Exhibit 10.1


                        AMENDMENT AND CONSENT TO GUARANTY


         AMENDMENT AND CONSENT TO UNCONDITIONAL GUARANTY dated as of July 1,
1999 between IRON MOUNTAIN INCORPORATED, a Delaware corporation (Guarantor) and
IRON MOUNTAIN STATUTORY TRUST - 1998, a Connecticut statutory trust
(Owner), and consented to by each of the Lenders and Agent Bank listed on the
signature pages hereto.

         Guarantor and Owner are parties to a certain Unconditional Guaranty
dated as of October 1, 1998 (the Original Guaranty) pursuant to which the
Guarantor guarantees to Owner and the Indemnified Parties the Guaranteed
Obligations, including, without limitation, certain obligations of Iron Mountain
Records Management, Inc. (Lessee/Agent) under (i) a Lease Agreement from Owner
to Lessee/Agent dated as of October 1, 1998 (the Lease), and (ii) an Agency
Agreement between Lessee/Agent and Owner dated as of October 1, 1998 (the Agency
Agreement). Each of the Lease the Agency Agreement have been assigned to the
Agent Bank pursuant to an Assignment of Lease and Agency Agreement from Owner to
Agent Bank and consented to by Lessee/Agent dated as of October 1, 1998.
Guarantor has requested that Owner amend the Original Guaranty with respect to
certain financial covenants and related definitions; and Guarantor has requested
that the Lenders and Agent Bank consent to such changes.
Accordingly, the parties hereto agree as follows:

         Section 1. DEFINITIONS. Except as otherwise defined in this Agreement,
terms defined in the Original Guaranty are used herein as defined therein.

         Section 2. AMENDMENTS. Subject to the terms and conditions contained
herein, the Original Guaranty is hereby amended as follows:

         A. GENERAL. The phrase "default or Event of Default" wherever used in
the Original Guaranty is hereby deleted and replaced with the following:
"Default or Event of Default".

         B. SECTION 2. The phrase "the Lease, the Agency Agreement or this
Guaranty" wherever used in Section 2, clauses (a), (c) through (e) and (h) of
the Original Guaranty is hereby deleted and replaced with the following: "the
Lease, the Agency Agreement, this Guaranty or any other Operative Document".


         C. LEVERAGE RATIO. The Leverage Ratio "grid" in Section 10(a)(i) of the
Original Guaranty is hereby amended to read as follows:



<PAGE>


<TABLE>
<CAPTION>

PERIOD                                           LEVERAGE RATIO
------                                           --------------
<S>                                              <C>
From July 1, 1999                                5.75 to 1
through December 31, 2000

From January 1, 2001                             5.50 to 1
through December 31, 2001

From January 1, 2002                             5.25 to 1
through June 30, 2002

From July 1, 2002                                5.00 to 1
and at all times thereafter

</TABLE>


         D. INTEREST COVERAGE RATIO. The Interest Coverage Ratio "grid" in
Section 10(a)(ii) of the Original Guaranty is hereby amended to read as follows:

<TABLE>
<CAPTION>

PERIOD                                           LEVERAGE RATIO
------                                           --------------
<S>                                              <C>
From January 1, 1999                             1.85 to 1
through December 31, 1999

From January 1, 2000                             2.00 to 1
through December 31, 2001

From January 1, 2002                             2.25 to 1
and at all times thereafter

</TABLE>


         E. FIXED CHARGES COVERAGE RATIO. The second paragraph of Section
10(a)(iii) of the Original Guaranty is hereby deleted in its entirety and
replaced as follows:

                  "For purposes of calculating any ratio set forth in this
                  clause (iii), if Guarantor elects pursuant to the penultimate
                  sentence of the definition of EBITDA to include in EBITDA for
                  the period to which such ratio relates the PRO FORMA amounts
                  referred to in such sentence, there shall be included in Fixed
                  Charges for such period, on a PRO FORMA basis, principal
                  payable and interest accruing during such period on
                  Indebtedness (and the interest portion of payments under
                  Capitalized Lease Obligations) assumed or incurred by
                  Guarantor and its Subsidiaries (on a consolidated basis) in
                  connection with any Permitted Acquisition having Acquisition
                  Consideration of more than $500,000 during such period."

         F.       LIENS.


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<PAGE>



                  a. Clause (iii) of Section 10(a)(iv) of the Original Guaranty
is hereby deleted in its entirety and replaced as follows:

                  "(iii)(A) Liens otherwise permitted by the Operative Documents
                  contemplated by or securing Indebtedness described in clauses
                  (ii), (iv), (v) and (vii) of the definition of Permitted
                  Indebtedness set forth in the Credit Agreement; and (B) Liens
                  securing Acquired Debt, provided that such Liens cover only
                  those assets that were covered by such Liens prior to the
                  relevant acquisition;"

                  b. Clause (viii) of Section 10(a)(iv) of the Original Guaranty
is hereby deleted in its entirety and replaced as follows:

                  "(viii) Liens arising under or created pursuant to the Lease
                  or the Lease Agreement between Iron Mountain Statutory Trust -
                  1999 and Lessee/Agent dated as of July 1, 1999."

         G.       DEFINITIONS.

                  a. Section 10(c) of the Original Guaranty is hereby amended by
inserting the following definitions (or, in the case of any definition for a
term that is defined in the Original Guaranty before giving effect to this
Agreement, by amending and restating such definition to read as set forth
below):

                           "ACQUIRED DEBT" shall have the meaning set forth in
                  the Credit Agreement.

                           "EXCLUDED SUBSIDIARY" shall mean any Subsidiary of
                  the Guarantor principally engaged in the records management
                  business organized outside the United States.

                           "FUNDED INDEBTEDNESS" shall mean, without
                  duplication, (a) Indebtedness (other than in respect of
                  Synthetic Lease Obligations) that matures or otherwise becomes
                  due more than one year after the incurrence thereof or is
                  extendible, renewable or refundable, at the option of the
                  obligor, to a date more than one year after the incurrence
                  thereof (including the current portion thereof), (b)
                  Indebtedness outstanding under the Credit Agreement and (c)
                  Synthetic Lease Obligations of Lessee and any Guarantees by
                  the Guarantor thereof.

                           "INTEREST EXPENSE" shall mean, for any period, the
                  sum (determined without duplication) of the aggregate amount
                  of interest accruing during such period on Indebtedness of the
                  Guarantor and its Subsidiaries (on a consolidated basis),
                  including the interest portion of rental or similar payments
                  under Capital


                                       -3-
<PAGE>



                  Lease Obligations and Synthetic Leases and any capitalized
                  interest, and excluding amortization of debt discount and
                  expense and interest paid in kind.

                           "PERSON" shall mean an individual, a corporation, a
                  company, a voluntary association, a partnership, a limited
                  liability company, a trust, an unincorporated organization or
                  a government agency or any agency, instrumentality or
                  political subdivision thereof.

                           "SYNTHETIC LEASE" shall mean a lease of property or
                  assets designed to permit the lessee (i) to claim depreciation
                  on such property or assets under U.S. tax law and (ii) to
                  treat such lease as an operating lease or not to reflect the
                  leased property or assets on the lessee's balance sheet under
                  GAAP.

                           "SYNTHETIC LEASE OBLIGATIONS" shall mean, with
                  respect to any Synthetic Lease, at any time, an amount equal
                  to the higher of (x) the aggregate termination value or
                  purchase price or similar payments in the nature of principal
                  payable thereunder and (y) the then aggregate outstanding
                  principal amount of the notes or other instruments issued by,
                  and the amount of the equity investment, if any, in, the
                  lessor under such Synthetic Lease.

                   b. The definition of "EBITDA" in Section 10(c) of the
Original Guaranty is hereby amended by restating clause (b)(iii) thereof as
follows: "(iii) Interest Expense for such period,".

                  c. The definition of "Indebtedness" in Section 10(c) of the
Original Guaranty is hereby amended by restating clause (iii) thereof as
follows: "(iii) Capital Lease Obligations and Synthetic Lease Obligations of
such Person;".

         H. SECTION 13. The phrase "Event of Default" as used in Section 13 of
the Original Guaranty is hereby deleted and replaced with the following:
"Default or Event of Default".

         Section 3. CONDITIONS OF EFFECTIVENESS. This Agreement shall become
effective as of the date hereof when, and only when, the Owner, the Lenders and
the Agent Bank shall have received a counterpart of this Agreement duly executed
by the parties hereto and payment of an amendment fee pursuant to a letter sent
by Guarantor to the Agent Bank dated as of July 1999.

         Section 4. REPRESENTATIONS AND WARRANTIES. Guarantor hereby represents
and warrants to Owner, Agent Bank, the Lenders and their respective counsel
that:


                                       -4-
<PAGE>



                  A. the representations and warranties made by Guarantor in
         each Operative Document to which it is a party are correct on and as of
         the date hereof, as though made on and as of such date (or, if any such
         representation or warranty is expressly stated to have been made as of
         a specific date, as of such specific date); and

                  B. no event has occurred and is continuing under any Operative
         Document that constitutes a Default or an Event of Default.

         Section 5. MISCELLANEOUS. Except as herein provided, the Original
Guaranty and each of the other Operative Documents shall remain unchanged and in
full force and effect. Upon the effectiveness of this Agreement, on and after
the date hereof, each reference in any Operative Document to the Original
Guaranty shall mean and be a reference to the Original Guaranty as amended
hereby. This Agreement may be executed in any number of counterparts, all of
which taken together shall constitute one and the same instrument and any of the
parties hereto may execute this Agreement by signing any such counterpart. This
Agreement shall be governed by, and construed in accordance with, the law of the
Commonwealth of Massachusetts.


         IN WITNESS WHEREOF, the parties hereunto have caused this Agreement to
be executed by their respective officers thereunto duly authorized, as of the
date first above written.

                                   GUARANTOR:

                                   IRON MOUNTAIN INCORPORATED

                                   By:   /s/ J.P. Lawrence
                                        -------------------------------------
                                        Name:    J.P. Lawrence
                                        Title:   Vice President and Treasurer



<PAGE>



AGREED AND CONSENTED TO:

AGENT BANK:

THE BANK OF NOVA SCOTIA,
as Agent Bank

By:   /s/ T.M. Pitcher
      ------------------------------
      Name:  T.M. Pitcher
      Title:    Authorized Signatory




                                       -6-
<PAGE>


LENDERS:


BANKBOSTON, N.A.                                    FLEET NATIONAL BANK


By:  /s/ James F. Law                           By:  /s/ Michael A. Palmer
     -------------------------------                 ------------------------
     Name:    James F. Law                           Name:  Michael A. Palmer
     Title:   Vice President                         Title: Vice President


UNION BANK OF CALIFORNIA, N.A.                      USTRUST


By:  /s/ Nancy A. Perkins                       By:  /s/ Daniel G. Eastman
     -------------------------------                 ------------------------
     Name:    Nancy A. Perkins                       Name:  Eastman D.G.
     Title:   Vice President                         Title: Vice President


THE BANK OF NOVA SCOTIA


By:  /s/ T.M. Pitcher
     ---------------------------
     Name:  T.M. Pitcher
     Title: Authorized Signatory



                                       -7-
<PAGE>


                    OWNER:

                    IRON MOUNTAIN STATUTORY TRUST - 1998

                    By:      First Union National Bank, not in its individual
                             capacity except as expressly set forth herein, but
                             solely as trustee under the Amended and Restated
                             Trust Agreement dated as of October 1, 1998

                             By:  /s/ Jeffrey Kramer
                                  ---------------------------------------------
                                  Name:    Jeffrey Kramer
                                  Title:   Vice President


                                       -8-