Increasing attention is being paid to the role of nutrition in cancer. Dietary measures, such as decreased consumption of calories, fat, alcohol and smoked or pickled foods have been shown to reduce the incidence of specific "adult" cancers, while increased dietary fiber appears to have a protective role. However, no clear scientific evidence exists that dietary manipulation is a successful primary therapy for established cancer. A significant percentage of adult and child cancer patients take unproven therapies during their illness. Alternative nutritional therapies, of which there is a wide variety, are the commonest of these reflecting current public interest in "natural" remedies. The efficacy and potential toxicity of commonly utilized dietary therapies are here reviewed, in particular the macrobiotic philosophy, the Gerson diet, the Livingstone diet, and the use of vitamin and mineral therapy. While details may differ, most alternative approaches involve fresh whole foods, with strong emphasis on low-fat vegetarian diet. Most are nutritionally adequate, at least for adults. No anti-cancer diet has been shown to cure established cancers, even those whose incidence is decreased by dietary changes. Careful dietary manipulation may at least improve quality of life for adult cancer patients, and, together with conventional therapy, may prolong survival in selected cancer patients. Assessment by carefully controlled prospective clinical trials is essential; those in pediatric patients must be controlled very strictly, since tumors in children have not been shown to be influenced by diet, and the diets described may be inadequate for children with malignant disease.