Malnutrition is a frequent problem in persons infected with the human immunodeficiency virus. The origin of malnutrition in patients with AIDS may be multifactorial. The primary mechanisms include disorders of food intake, alterations in intermediary metabolism, and nutrient malabsorption. Attention to the problems of malnutrition in patients with AIDS is of paramount importance because the timing of death in these patients may be more closely related to degree of body cell mass depletion than to any specific underlying infection. Nutritional support can improve nutritional status in selected patients, and repletion of body cell mass may be associated with functional improvement. Early assessment, attention to nutritional requirements, and prompt intervention can minimize wasting and replete body cell mass. This article examines the evidence for malnutrition in patients with AIDS, reviews the studies of nutritional support, and presents an approach to the management of malnutrition in AIDS.