This filing is made pursuant to Rule 424(b)(3) under the Securities Act of 1933 in connection with Registration No. 333-71896. PROSPECTUS SUPPLEMENT NO. 20 TO PROSPECTUS DATED JANUARY 15, 2002 LABORATORY CORPORATION OF AMERICA HOLDINGS $744,000,000 Aggregate Principal Amount at Maturity of Liquid Yield Option(TM) Notes due 2021 (Zero Coupon - Subordinated) and Common Stock issuable upon Conversion or Purchase of the LYONs ------------------------------------------- This prospectus supplement will be used by the holders of LYONs listed below to resell their LYONs or the shares of our common stock, par value $0.10 per share, issuable upon conversion or purchase of the LYONs. You should read this prospectus supplement together with the prospectus dated January 15, 2002, which is to be delivered with this prospectus supplement. The table below sets forth additional and updated information concerning beneficial ownership of the LYONs, and supplements and, to the extent inconsistent with, amends the table appearing under the caption "Selling Securityholders" beginning on page 37 of the prospectus. To the extent that a selling securityholder is listed both in the table below and in the table appearing in the prospectus, the information set forth below regarding that selling securityholder supersedes the information set forth in the prospectus. We have prepared this table based on information given to us by the selling securityholders listed below prior to the date hereof. Aggregate Percentage Principal Percentage Number of of Amount of Shares Common at Maturity LYONs of Common Stock of LYONs Outstanding Stock Owned Outstanding Owned and Prior to and that Prior that May the May be to the Name be Sold Offering Sold(1) Offering(2) -------------------------- ---------- ----------- ------------ ----------- The Northwestern Mutual Life Insurance Company - General Account $9,500,000 1.28% 127,402 * The Northwestern Mutual Life Insurance Company - Group Annuity Separate Account 500,000 * 6,705 * ---------------------- * Less than 1%. (1) Assumes conversion of all of the holder's LYONs at a conversion rate of 13.4108 shares of common stock per $1,000 principal amount at maturity of the LYONs as a result of a 2-for-1 forward split on May 10, 2002. This conversion rate is subject to adjustment, however, as described under "Description of LYONs - Conversion Rights - Conversion Adjustments and Delivery of Common Stock" beginning on page 16 of the prospectus. As a result, the number of shares of common stock issuable upon conversion of the LYONs may increase or decrease in the future. (2) Calculated based on Rule 13d-3(d)(1)(i) of the Exchange Act using 148,030,874 shares of common stock outstanding as of March 11, 2003. In calculating this amount for each holder, we treated as outstanding the number of shares of common stock issuable upon conversion of all of that holder's LYONs, but we did not assume conversion of any other holder's LYONs. ------------------------------------------- Investing in the LYONs involves risks that are described in "Risk Factors Relating to the LYONs" beginning on page 8 of the prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved these securities, or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense. The date of this prospectus supplement is March 12, 2003 (TM)Trademark of Merrill Lynch & Co., Inc.