Wasting syndrome is a common complication of HIV infection and is marked by progressive weight loss and weakness, often associated with fever and diarrhea. The pathophysiologic mechanisms responsible for this syndrome are not well defined, but it is clear that this is a multifactorial process in which the relative contribution of individual etiologic factors vary among patients. Considerations include inadequate diet, malabsorptive phenomena, metabolic derangements, and cytokine activity. The onset of opportunistic infections is often accompanied by a hypermetabolic state characterized by progressive weight loss. Potential cytokines that may promote weight loss in AIDS patients include tumor necrosis factor, interleukin-1, interleukin-6, and alpha-interferon. At present there is no effective treatment. Multiple therapeutic methods, including enteral and parenteral alimentation, appetite stimulants, recombinant growth hormone, and cytokine modulators, are currently being explored.