Involuntary weight loss with lean tissue depletion is a serious and AIDS-defining complication of HIV infection. This article explores definitions of AIDS wasting syndrome (AWS), its etiology, methods of assessing body composition, and pharmacological treatments. Recent research literature on the role of exercise in the prevention and treatment of AWS is reviewed. Included are studies of the safety of exercise, the effects of exercise on the immune system, and the effects of exercise on weight gain and body composition as well as studies of exercise in combination with medications and other interventions. Implications for clinical practice are discussed.