<PAGE>   1
                                                                    Exhibit 12.1
                        WORLDCOM, INC. AND SUBSIDIARIES
          Computation of Ratio of Earnings to Combined Fixed Charges
                         and Preferred Stock Dividends
                           (In Thousands of Dollars)



<TABLE>
<CAPTION>
                                                                               Year Ended December 31,
                                                   -------------------------------------------------------------------------------
                                                                        Historical                              Pro Forma
                                                   -------------------------------------------------------------------------------
                                                     1992     1993      1994        1995       1996          1995         1996
                                                   -------- --------- ---------  ---------- ------------  ----------  ------------
Earnings:
<S>                                                <C>      <C>       <C>        <C>        <C>           <C>         <C>
  Pretax income (loss) from continuing operations  $ 20,401 $ 198,237 $ (78,463) $  404,538 $ (2,060,276) $ (193,089) $ (2,762,906)
  Fixed charges, net of capitalized interest         38,720    58,999    87,455     300,248      242,257     364,742       390,008
                                                   -------- --------- ---------  ---------- ------------  ----------  ------------

  Earnings                                         $ 59,121 $ 257,236 $   8,992  $  704,786 $ (1,818,019) $  171,653  $ (2,372,898)
                                                   ======== ========= =========  ========== ============  ==========  ============

Fixed charges:
  Interest cost                                    $ 33,815 $  38,657 $  49,203  $  254,099 $    229,376  $  312,155  $    353,085
  Amortization of financing costs                     1,464     1,792     2,086       2,811        1,742       2,811             -
  Interest factor of rent expense                     4,833     9,967    10,300      15,030       17,854      25,200        28,024
  Preferred dividend requirements                     2,112    11,683    27,766      33,191          860      48,255        30,289
                                                   -------- --------- ---------  ---------- ------------  ----------  ------------

  Fixed charges                                    $ 42,224 $  62,099 $  89,355  $  305,131 $    249,832  $  388,421  $    411,398
                                                   ======== ========= =========  ========== ============  ==========  ============
Deficiency of earnings to combined fixed charges
  and preferred stock dividends                    $      - $       - $ (80,363) $        - $ (2,067,851) $ (216,768) $ (2,784,296)
                                                   ======== ========= =========  ========== ============  ==========  ============
Ratio of earnings to combined fixed charges and
  preferred stock dividends                          1.40:1    4.14:1    0.10:1      2.31:1      N/A           0.44:1      N/A
                                                   ======== ========= =========  ==========  ============  ========== ============
</TABLE>


See Notes to Computation of Earnings to Combined Fixed Charges and Preferred
Stock Dividends
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                  NOTES TO COMPUTATION OF RATIO OF EARNINGS TO
              COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS


(1)      On December 31, 1996, WorldCom completed the MFS Merger.  The MFS
         Merger is being accounted for as a purchase; accordingly, the
         operating results for MFS are not reflected in the historical amounts
         above and will be included from the date of acquisition.

(2)      Results for 1996 include a $2.14 billion charge for in-process
         research and development related to the MFS Merger.  The charge is
         based upon a valuation analysis of the technologies of MFS' worldwide
         information system, the Internet network expansion system of UUNET, and
         certain other identified research and development projects purchased in
         the Merger.  The expense includes $1.6 billion associated with UUNET
         and $0.54 billion related to MFS.

         Additionally, 1996 results include other after-tax charges of $121
         million for employee severance, employee compensation charges,
         alignment charges, and costs to exit unfavorable telecommunications
         contracts and $344 million after-tax write-down of operating assets
         within its non-core businesses.  On a pre-tax basis, these charges 
         totaled $600.1 million.

(3)      In 1995, Metromedia converted its Series 1 Preferred Stock into Common
         Stock, exercised warrants to acquire Common Stock and immediately sold
         its position of 61,699,096 shares of Common Stock in a public
         offering.  In connection with the preferred stock conversion, WorldCom
         made a non-recurring payment of $15.0 million to Metromedia,
         representing a discount to the minimum nominal dividends that would
         have been payable on the Series 1 Preferred Stock prior to the
         September 15, 1996 optional call date of approximately $26.6 million
         (which amount includes an annual dividend requirement of $24.5 million
         plus accrued dividends to such call date).

(4)      As a result of the IDB Merger and the ATC Merger, the Company
         initiated plans to reorganize and restructure its management and
         operational organization and facilities to eliminate duplicate
         personnel, physical facilities and service capacity, to abandon
         certain products and marketing activities, and to take further
         advantage of the synergies available to the combined entities.  Also,
         during the fourth quarter of 1993, plans were approved to reduce IDB's
         cost structure and to improve productivity.  Accordingly, in 1994,
         1993 and 1992, the Company charged to operations the estimated costs
         of such reorganization and restructuring activities, including
         employee severance, physical facility abandonment and duplicate
         service capacity.  These costs totaled $43.7 million in 1994, $5.9
         million in 1993 and $79.8 million in 1992.

         Also, during 1994 and 1992, the Company incurred direct merger costs
         of $15.0 million and $7.3 million, respectively, related to the IDB
         Merger (in 1994) and the ATC Merger (in 1992).  These costs include
         professional fees, proxy solicitation costs, travel and related
         expenses and certain other direct costs attributable to these mergers.

(5)      In connection with certain debt refinancing, the Company recognized in
         1996, 1993 and 1992 extraordinary items of approximately $4.2 million,
         $7.9 million and $5.8 million, respectively, net of income taxes,
         consisting of unamortized debt discount, unamortized issuance cost and
         prepayment fees.  Additionally, in 1996 the Company recorded an
         extraordinary item of $20.2 million, net of income taxes, related to a
         write-off of deferred international costs.