This article summarizes the U.S. Preventive Services Task Force (USPSTF) recommendations on routine vitamin supplementation to prevent cancer and cardiovascular disease and the supporting scientific evidence. The USPSTF concludes that the evidence is insufficient to recommend for or against the use of supplements of vitamins A, C, or E; multivitamins with folic acid; or antioxidant combinations for the prevention of cancer or cardiovascular disease. Also, the USPSTF recommends against the use of beta-carotene supplements, either alone or in combination, for the prevention of cancer or cardiovascular disease.