Central nervous system (CNS) manifestations are common in patients with the acquired immunodeficiency syndrome (AIDS). The most common CNS syndrome is a dementing illness referred to as the AIDS dementia complex, in which motor and cognitive changes may also be seen. Neurodiagnostic studies are fairly characteristic, though highly nonspecific. Dementia may precede overt manifestations of AIDS, and either an insidious or a fulminant course may be seen. Appropriate management of the patient with AIDS includes differentiating dementia from psychologic responses to the disease.