A common complication of acquired immunodeficiency syndrome (AIDS) is being increasingly recognized. Known as AIDS dementia complex, the disorder is characterized by global impairment of intellectual and cognitive functions, personality and behavioral disturbances, and motor dysfunction manifested by impaired speech, gait, and coordination. AIDS dementia complex progresses rapidly and inexorably from psychomotor slowing to dementia, then to an akinetic mute state in which the patient becomes immobile and incapable of speaking, and finally to coma. Differentiation of AIDS dementia complex from a potentially treatable condition, such as reactive depression, is important. Zidovudine (Retrovir), the drug currently used to treat AIDS, has shown promise in the treatment of AIDS dementia complex. Clinical trials are now under way to determine its efficacy in this application.