Exhibit 11

                          IRON MOUNTAIN INCORPORATED 

                   Computation of Earnings per Common Share 


                (Amounts in thousands, except per share data) 





                                                                                  Six Months Ended 
                                             Year Ended December 31,                  June 30, 
                                   --------------------------------------------   ---------------- 
                                    1991     1992    1993     1994       1995      1995      1996 
                                   -------    ----    ----    ------    -------    ------   ------ 
                                                                       
Weighted Average Shares 
  Outstanding: 

 Common Stock                          --      --      --        --         --        --     7,987 
 Non-Voting Common Stock               --      --      --        --         --        --       415 
 Class A Common Stock                  --      14      29        29         38        31         8 
 Class C Common Stock                 266     266     266       185         --        --        -- 
 Series A1 Preferred Stock          2,962   2,962   2,962     1,152        556       988        22 
 Series A2 Preferred Stock             --      --      --     1,808      1,948     1,961       330 
 Series A3 Preferred Stock             --      --      --        --        432        --       146 
 Series C Preferred Stock           4,810   4,810   4,810     4,810      4,810     4,810       819 
                                    -----   -----   -----     -----      -----     -----      ---- 

Weighted Average Common Shares 
  Outstanding                       8,038   8,052   8,067     7,984      7,784     7,790     9,727 

Dilutive Effect of Stock 
  Options Considered Common 
  Stock Equivalents Computed 
  under the Treasury Stock 
  Method Using the Average 
  Price                               --       --      --        --         --        --       172 
                                    -----   -----   -----     -----      -----     -----      ---- 

Weight Average Common and 
  Common Equivalent Shares 
  Outstanding                       8,038   8,052   8,067     7,984      7,784     7,790     9,899 
                                    =====   =====   =====     =====      =====     =====     =====                             
Net Income (Loss) Applicable 
  to Common Stockholders          ($1,814) $  961  $  628   ($  128)   ($1,859)  ($  533)   $  417 
                                   ======  ======  ======    ======     ======    ======    ======                             

Net Income (Loss) per Common                                                                 
  and Common Equivalent Share     ($ 0.23) $ 0.12  $ 0.08   ($ 0.02)   ($ 0.24)  ($ 0.07)   $ 0.04
                                   ======  ======  ======    ======     ======    ======    ======