Data exist in the scientific literature showing reduction in the risk of tumor occurrence achieved by the use of nutritional and other natural materials. However, many trials that have attempted to prevent cancer occurrence with nutritional supplementation have found no effect or even increased tumor incidence. Several factors appear to be responsible for these disparate data, including the forms of nutrients used and the types of cancer being studied. In addition, combinations of nutrients have often been found to be more effective than single nutrient interventions. Appropriate use of supplemental nutrition, along with attention to pertinent dietary and lifestyle risk factors, comprise for the average person perhaps the best presently available strategy for prevention of the common types of malignancy.