Progressive dementia has been recognized as a complication of human immunodeficiency virus infection almost since the beginning of the epidemic. To many infectious diseases clinicians, however, the AIDS dementia complex remains ambiguous, and the clinical approach to this problem is less clearly defined than that for other infection-associated syndromes. Dr. Richard W. Price and his colleagues at Memorial Sloan-Kettering Cancer Center have, to a large extent, been responsible for defining this entity. In this AIDS Commentary they present their views of the current state of knowledge regarding the etiology, clinical presentation, and diagnostic and therapeutic approaches to the AIDS dementia complex.