<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>
                                       Six Months Ended                                  Years Ended
                                           June 30,                                      December 31,
                                       ----------------     ---------------------------------------------------------------
(Millions)                                   1998            1997           1996          1995          1994          1993
                                            ------          ------         ------        ------        ------        ------
<S>                                       <C>              <C>             <C>           <C>           <C>           <C>       
Pretax income (loss) from                              
 continuing operations                    $   712.0        $ 1,511.2       $   338.7     $   726.2     $   627.5     $(1,014.7)
                                                       
Add back fixed charges                        165.4            321.9           245.1         187.0         170.8         154.7
Minority interest                                .9             14.7            16.4          16.1          11.4           7.0
                                          ---------        ---------       ---------     ---------     ---------     ---------
                                                       
   Income (loss) as adjusted              $   878.3        $ 1,847.8       $   600.2     $   929.3     $   809.7     $  (853.0)
                                          =========        =========       =========     =========     =========     =========
                                                       
Fixed charges:                                         
  Interest on indebtedness (1)            $   113.4        $   235.8       $   168.3     $   115.9     $    98.6     $    77.4
 Portion of rents representative                       
   of interest factor                          52.0             86.1            76.8          71.1          72.2          77.3
                                          ---------        ---------       ---------     ---------     ---------     ---------
                                                       
 Total fixed charges                      $   165.4        $   321.9       $   245.1     $   187.0     $   170.8     $   154.7
                                          =========        =========       =========     =========     =========     =========
                                                       
Preferred stock dividend                               
 requirements                                  45.5             92.9            41.1          --            --            --
                                          ---------        ---------       ---------     ---------     ---------     ---------
Total combined fixed charges                           
and preferred stock dividend                           
 requirements                             $   211.0        $   414.3       $   286.2     $   187.0     $   170.8     $   154.7
                                          =========        =========       =========     =========     =========     =========
                                                       
Ratio of earnings to fixed                             
charges                                        5.31             5.74            2.45          4.97          4.74         (5.51)
                                          =========        =========       =========     =========     =========     =========
                                                       
Ratio of earnings to combined                          
 fixed charges and preferred                           
 stock dividends                               4.16             4.46            2.10          4.97          4.74         (5.51)
                                          =========        =========       =========     =========     =========     =========
</TABLE>                         

(1)      For the six months ended June 30, 1998 and years ended December 31,
         1997, 1996, 1995 and 1994, interest on indebtedness includes the
         dividends paid to preferred shareholders of a subsidiary. (See Note 14
         of Notes to Financial Statements in the Company's 1997 Annual Report.)




<PAGE>   2




                                                          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>
                                                          Six Months Ended            Years Ended
                                                              June 30,                 December 31,
                                                              --------                 ------------
                                                                             
(Millions)                                                      1998              1997             1996
----------                                                      ----              ----             ----
<S>                                                           <C>               <C>             <C>      
Pretax income from continuing                                                
 operations                                                   $   635.1         $ 1,505.2       $   335.0
                                                                             
Add back fixed charges                                            163.3             318.1           243.8
Minority interest                                                    .4              15.7            16.4
                                                              ---------         ---------       ---------
                                                                             
 Income as adjusted                                           $   798.8         $ 1,839.9       $   595.2
                                                              =========         =========       =========
                                                                             
Fixed charges:                                                               
  Interest on indebtedness (2)                                $   113.4         $   234.0       $   168.3
  Portion of rents representative                                            
   of interest factor                                              49.9              84.1            75.5
                                                              ---------         ---------       ---------
                                                                             
    Total fixed charges                                       $   163.3         $   318.1       $   243.8
                                                              =========         =========       =========
                                                                             
Preferred stock dividend                                                     
  requirements                                                     --                --              --
                                                              ---------         ---------       ---------
                                                                             
Total combined fixed charges                                                 
 and preferred stock dividend                                                
  requirements                                                $   163.3         $   318.1       $   243.8
                                                              =========         =========       =========
                                                                             
Ratio of earnings to fixed                                                   
  charges                                                          4.89              5.78            2.44
                                                              =========         =========       =========
                                                                             
Ratio of earnings to combined                                                
 fixed charges and preferred                                                 
  stock dividends                                                  4.89              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 13 of Notes to Financial
         Statements in the Company's 1997 Annual Report.)

(2)      Includes the dividends paid to preferred shareholders of a
         subsidiary.(See Note 14 of Notes to Financial Statements in the
         Company's 1997 Annual Report.)