<PAGE>

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                       SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549


                                  FORM 10-Q/A

(Mark One)
---
|x|       QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
---       EXCHANGE ACT OF 1934

          For the Quarterly Period Ended September 30, 1999

                                       or

       TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
       EXCHANGE ACT OF 1934

       For the transition period ______________ to ________________

       Commission file number 0-20763


                             McLEODUSA INCORPORATED
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                                           <C>

              Delaware                                    42-1407240
       (State of Incorporation)                (IRS Employer Identification No.)


     McLeodUSA Technology Park
         6400 C Street SW
         P.O. Box 3177
         Cedar Rapids, Iowa                               52406-3177
(Address of principal executive office)                   (Zip Code)
</TABLE>

                                  319-364-0000
                        (Registrant's telephone number,
                              including area code)

    Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
                                               ---
filing requirements for the past 90 days.  Yes |x|       No
                                               ---

    The number of shares outstanding of each class of the issuer's common stock
as of November 2, 1999:

     Common Stock Class A:  ($.01 par value).........  155,298,043 shares

     Common Stock Class B:  ($.01 par value).........        None

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                               EXPLANATORY NOTE

    Exhibit 27.1 to the Quarterly Report on Form 10-Q of McLeodUSA Incorporated
(File Number 0-20763) for the quarterly period ended September 30,
1999, filed with the SEC on November 15, 1999, is hereby amended and restated in
its entirety by the information set forth herein on Exhibit 27.1 to this Form
10-Q/A. Exhibit 27.1 has been amended to reflect a [MULTIPLIER] of 1,000 and to
apply such [MULTIPLIER] to the information presented.

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                                  SIGNATURES

    Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

                                    McLEODUSA INCORPORATED
                                    (registrant)


Date:  November 16, 1999            By:       /s/ Stephen C. Gray
                                        --------------------------------------
                                                 Stephen C. Gray
                                        President and Chief Operating Officer


Date:  November 16, 1999            By:       /s/ J. Lyle Patrick
                                        --------------------------------------
                                                 J. Lyle Patrick
                                             Chief Financial Officer

                                       3

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                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
                                                                    Sequentially
 Exhibit                                                             Numbered
 Number    Exhibit Description                                         Page
---------  -------------------                                      ------------
<S>        <C>                                                          <C>
  27.1     Financial Data Schedule.
</TABLE>

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