Approximately 90 epidemiologic studies have examined the role of vitamin C or vitamin-C-rich foods in cancer prevention, and the vast majority have found statistically significant protective effects. Evidence is strong for cancers of the esophagus, oral cavity, stomach, and pancreas. There is also substantial evidence of a protective effect in cancers of the cervix, rectum, and breast. Even in lung cancer, for which carotenoids show a consistent protective effect, there is recent evidence of a role for vitamin C. Vitamin C is an important antioxidant and free radical scavenger in plasma and acts to regenerate active vitamin E in lipid membranes. Although several different factors in fruits and vegetables probably act jointly, the epidemiologic and biochemical evidence indicate an important role for vitamin C.