<PAGE>
 
================================================================================

                                                                    Exhibit 11.1

                          LaSalle Re Holdings Limited

            Statement of Computation of Net Income per Common Share

               (Expressed in thousands of United States Dollars
              except for number of shares and earnings per share)
                                   Unaudited
<TABLE>
<CAPTION>
 
                                                        Quarter ended           Nine months        
                                                        June 30, 1997        ended June 30,1997    
                                                       --------------        ------------------    
<S>                                               <C>                        <C>                          
                                                                                                               
                                                                   Fully                    Fully      
                                                  Primary         Diluted     Primary      Diluted     
                                                  -------         -------     -------      -------     
                                                                                                       
Net income before minority interest:(1)            37,685          37,685      98,430       98,430     
Preferred dividend                                 (1,641)         (1,641)     (1,741)      (1,741)    
                                               ----------      ----------  ----------    ---------     
Net income available to common                                                                         
  shareholders                                     36,044          36,044      96,689       96,689     
                                               ==========      ==========  ==========    =========
Number of shares:                                                                             
                                                                                              
Weighted average shares                                                                       
outstanding                                    15,635,182      15,635,182  15,734,587   15,734,587 
Exchangeable non-voting shares     (1)          4,888,018       4,888,018   6,263,523    6,263,523
Incremental shares of outstanding  
stock options                      (2)          1,579,785       1,592,412   1,511,357    1,616,370
Incremental shares of outstanding
stock appreciation rights          (3)             66,544          69,069      60,262       69,069
                                               ----------      ----------  ----------   ----------
                                               22,169,529      22,184,681  23,569,729   23,683,549
                                               ==========      ==========  ==========   ========== 
Earnings per share:                                  1.63            1.62        4.10         4.08
</TABLE>

(1)  The holders of exchangeable non-voting shares in LaSalle Re Limited, which
     represents the minority interest, generally can exchange these shares at
     any time, on a one for one basis, for common shares in LaSalle Re Holdings
     Limited. For purposes of the computation of net income per common share,
     the weighted average shares outstanding have been treated as common share
     equivalents. 

(2)  As of June 30, 1997, the Company had 2,686,887 options outstanding. The
     dilution would be the equivalent of approximately 1,579,785 shares for the
     quarter and 1,511,357 for the nine months ended June 30, 1997, using the
     treasury stock method, based on average market price.

(3)  As of March 31, 1997, the Company had granted 340,872 stock appreciation
     rights. The dilution would be the equivalent of approximately 66,544 shares
     for the quarter ended June 30, 1997 and 60,262 for the nine months ended
     June 30, 1997, using the treasury stock method, based on average market
     price.


===============================================================================