Patients with malignancies which are treated with therapeutic radiation are at risk for nutritional problems, both from their underlying malignancy as well as from their treatment. These effects may be acute or chronic and relate to the site of the tumor and regions irradiated. There is a large experience with nutritional intervention in irradiated patients, including oral feedings and enteral and parenteral nutritional support. The indications for the specific administration of nutritional support during radiotherapy depend on the nutritional status of the patient and the area irradiated, as well as the individual prognosis. Patients who are malnourished at the time of treatment are most likely to profit from nutritional intervention. To date, prospective randomized trials of nutritional support in patients undergoing radiotherapy fail to show a benefit of routine adjuvant nutritional intervention in terms of improved response and tolerance to treatment, improved local control or survival rates, or reduction of complications from therapy.