An abundance of epidemiologic evidence, based on numerous and remarkably consistent observations that persons who consume high intakes of fruits and vegetables have reduced risks of most human cancers, supports the concept that micronutrients may play important roles in the prevention of human cancers. Many studies suggest that carotenoid compounds in fruits and vegetables may be important in reducing risk of lung cancer. At least some forms of fiber may contribute to reduced risk of colon cancer, but recent analyses of colonic polyps suggest that folic acid may also play a protective role. Evidence for breast cancer is more limited but protective associations with vitamin A from both carotenoid and preformed sources have been seen in several studies. Although we cannot be certain which compounds are responsible, the evidence is overwhelming that an abundant intake of fruits and vegetables can play an important role in reducing cancer incidence.