The interactions of cancer and malnutrition are discussed with the focus on aging. To establish whether the elderly are more likely to develop cancer cachexia and its complications, this review encompasses the pathogenesis of malnutrition in cancer; the age-related alterations of appetite, gastrointestinal function, energy expenditure, and protein turnover; the diagnosis of malnutrition; and the effectiveness of nutritional support in the elderly. Although metabolic and physiologic changes induced by cancer and age appear synergistic in causing cachexia, more frequent complications of malnutrition have not been observed in the geriatric cancer patients. This may be due to only a small proportion of the elderly with cancer being enrolled in clinical studies or to a reduced cachexia-inducing ability of tumors in these patients. A limited number of studies indicate nutritional replenishment is obtainable in malnourished elderly by hyperalimentation. As restoration of the lean body mass may be slower in older patients, early institution of nutritional support is recommended in malnourished elderly or elderly at risk for malnutrition during neoplastic treatment.