<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,
                                                       -----------------------------------------------------------
                                                         1993       1994        1995         1996          1997
                                                       --------   --------    --------   -----------    ----------
<S>                                                    <C>        <C>         <C>        <C>            <C>
Earnings:
  Pretax income (loss) from continuing operations      $198,237   $(78,463)   $404,538   $(2,060,276)   $  799,273
  Fixed charges, net of capitalized interest             58,999     87,455     300,248       242,257       394,448
                                                       --------   --------    --------   -----------    ----------

  Earnings                                             $257,236   $  8,992    $704,786   $(1,818,019)   $1,193,721
                                                       ========   ========    ========   ===========    ==========

Fixed charges:
  Interest cost                                        $ 38,657   $ 49,203    $254,099   $   229,376    $  403,950
  Amortization of financing costs                         1,792      2,086       2,811         1,742         4,673
  Interest factor of rent expense                         9,967     10,300      15,030        17,854        43,592
  Preferred dividend requirements                        11,683     27,766      33,191           860        26,433
                                                       --------   --------    --------   -----------    ----------

  Fixed charges                                        $ 62,099   $ 89,355    $305,131   $   249,832    $  478,648
                                                       ========   ========    ========   ===========    ==========
Deficiency of earnings to combined fixed charges and
  preferred stock dividends                            $     --   $(80,363)   $     --   $(2,067,851)           --
                                                       ========   ========    ========   ===========    ==========
Ratio of earnings to combined fixed charges and
  preferred stock dividends                              4.14:1     0.10:1      2.31:1           N/A        2.49:1
                                                       ========   ========    ========   ===========    ==========
</TABLE>


See Notes to Computation of Ratio 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)      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 an
         independent appraisal, which valued 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 $121.0
         million for employee severance, employee compensation charges,
         alignment charges, and costs to exit unfavorable telecommunications
         contracts and $343.5 million after-tax write-down of operating assets
         within its core and non-core business. On a pre-tax basis, these
         charges totaled $600.1 million.

(2)      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
         included an annual dividend requirement of $24.5 million plus accrued
         dividends to such call date).

(3)      As a result of the IDB 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 and 1993, 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 and $5.9 million in 1993.

         Also, during 1994, the Company incurred direct merger costs of $15.0
         million related to the IDB Merger. These costs include professional
         fees, proxy solicitation costs, travel and related expenses and certain
         other direct costs attributable to the IDB Merger.

(4)      In connection with certain debt refinancing, the Company recognized in
         1996 and 1993 extraordinary items of approximately $4.2 million and
         $7.9 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.