Malnutrition, a common problem in cancer patients, adversely affects survival and quality of life. It results from several factors that alter nutritional intake and cause massive metabolic disturbances. Anticancer therapies may compound the malnutrition. Optimal nutrition improves therapeutic modalities and the clinical course and outcome. Oral nutrition should be used whenever possible; in patients unable to ingest adequate amounts orally, enteral and parenteral feedings are safe and effective.