<PAGE>   1
                                                                      Exhibit 12


AETNA INC.

COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF EARNINGS
TO COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS

<TABLE>
<CAPTION>
                                       Three Months Ended                            Years Ended
                                            March 31,                                December 31,
                                       ------------------    -----------------------------------------------------------
 (Millions)                                   1999              1998         1997         1996        1995        1994
------------------------------------------------------------------------------------------------------------------------
<S>                                    <C>                   <C>          <C>          <C>         <C>         <C>      
Pretax income from                                          
  continuing operations                    $   300.3         $ 1,408.3    $ 1,511.2    $   338.7   $   726.2   $   627.5
                                                            
Add back fixed charges                          95.3             358.5        321.9        245.1       187.0       170.8
Minority interest                                5.5              10.7         14.7         16.4        16.1        11.4
------------------------------------------------------------------------------------------------------------------------
                                                            
   Income as adjusted                      $   401.1         $ 1,777.5    $ 1,847.8    $   600.2   $   929.3   $   809.7
========================================================================================================================
                                                            
Fixed charges:                                              
  Interest on indebtedness (1)             $    64.6         $   250.9    $   235.8    $   168.3   $   115.9   $    98.6
  Portion of rents representative                           
    of interest factor                          30.7             107.6         86.1         76.8        71.1        72.2
------------------------------------------------------------------------------------------------------------------------
                                                            
Total fixed charges                        $    95.3         $   358.5    $   321.9    $   245.1   $   187.0   $   170.8
========================================================================================================================
                                                            
  Preferred stock dividend                                  
  requirements                                  23.1              92.2         92.4         41.1          --          --
------------------------------------------------------------------------------------------------------------------------
  Total combined fixed charges                              
  and preferred stock dividend                              
    requirements                           $   118.4         $   450.7    $   414.3    $   286.2   $   187.0   $   170.8
========================================================================================================================
                                                            
  Ratio of earnings to fixed                                
    charges                                     4.21              4.96         5.74         2.45        4.97        4.74
========================================================================================================================
                                                            
  Ratio of earnings to combined                             
  fixed charges and preferred                               
  stock dividends                               3.39              3.94         4.46         2.10        4.97        4.74
========================================================================================================================
</TABLE>

(1)  Includes the dividends paid to preferred shareholders of a subsidiary. (See
     Note 15 of Notes to Consolidated Financial Statements in the Company's 1998
     Annual Report.)


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                                                          Exhibit 12 (Continued)
AETNA SERVICES, INC. (1)

COMPUTATION OF RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF EARNINGS TO
COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS

<TABLE>
<CAPTION>
                                                  Three Months Ended                        Years Ended
                                                      March 31,                             December 31,
                                                  ------------------        ------------------------------------------
  (Millions)                                             1999                 1998              1997            1996
  --------------------------------------------------------------------------------------------------------------------
<S>                                               <C>                       <C>              <C>               <C>    
  Pretax income from continuing operations              $187.9              $ 1,162.7        $ 1,505.2         $ 335.0

  Add back fixed charges                                  94.3                  354.3            318.1           243.8
  Minority interest                                        4.9                   10.8             15.7            16.4
  --------------------------------------------------------------------------------------------------------------------

  Income as adjusted                                    $287.1              $ 1,527.8        $ 1,839.0         $ 595.2
  ====================================================================================================================

  Fixed charges:                                                                                       
    Interest on indebtedness (2)                         $64.6                $ 250.9          $ 234.0         $ 168.3
    Portion of rents representative                                                                    
     of interest factor                                   29.7                  103.4             84.1            75.5
  --------------------------------------------------------------------------------------------------------------------

      Total fixed charges                                $94.3                $ 354.3          $ 318.1         $ 243.8
  ====================================================================================================================

  Preferred stock dividend requirements                     --                     --               --              --
  --------------------------------------------------------------------------------------------------------------------

  Total combined fixed charges and preferred
     stock dividend requirements                         $94.3                $ 354.3          $ 318.1         $ 243.8
  ====================================================================================================================

  Ratio of earnings to fixed charges                      3.04                   4.31             5.78            2.44
  ====================================================================================================================

  Ratio of earnings to combined fixed charges
       and preferred stock dividends                      3.04                   4.31             5.78            2.44
  ====================================================================================================================
</TABLE>

(1)  Aetna Inc. has fully and unconditionally guaranteed the payment of all
     principal, premium, if any, and interest on all outstanding debt securities
     of Aetna Services, Inc. (See Note 14 of Notes to Financial Statements in
     the Company's 1998 Annual Report.)

(2)  Includes the dividends paid to preferred shareholders of a subsidiary.(See
     Note 15 of Notes to Consolidated Financial Statements in the Company's 1998
     Annual Report.)


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