BACKGROUND: Reduction of cancer risk by either preventing carcinogenesis or stopping carcinogenesis in its early stages is a logical approach for reducing the cancer burden, both for high-risk individuals and for the general population. The areas of dietary modification and chemoprevention show considerable promise as effective approaches for cancer prevention and are a focus of research efforts. RESULTS: Diet and cancer studies show that, generally, vegetables and fruits, dietary fiber, and certain nutrients seem to be protective against cancer, whereas fat, excessive calories, and alcohol seem to increase cancer risk. Chemoprevention research is closely linked to diet and cancer research and represents a logical research progression. CONCLUSIONS: Dietary epidemiologic studies have helped to identify many naturally occurring chemopreventive agents. Currently, randomized clinical prevention trials sponsored by the NCI include dietary interventions (eg, low-fat and/or high-fiber vegetables and fruits) targeting breast and colorectal cancer, chemoprevention trials using micronutrients (eg, vitamin E, calcium, vitamin D) aimed at lung and colorectal cancer, and chemoprevention trials testing the effectiveness of pharmaceutical agents (eg, tamoxifen, finasteride, aspirin) for breast, prostate, and colorectal cancer.