A group of 34 homosexual men with acquired immune deficiency syndrome (AIDS) spectrum disorders were assessed for cognitive impairment on a range of neuropsychological tests. There were 17 patients with AIDS, and 17 with AIDS-related complex (ARC). Although none of the patients showed signs of the severe dementing syndrome that has been described in persons with HIV infection, they demonstrated signs of cognitive impairment consistent with organic brain dysfunction. The profile of deficits shown by AIDS and ARC patients could be broadly grouped into disorders of recent and delayed memory and learning, generalized cognitive slowing, and reduced mental flexibility. Considerations of the clinical and neuropathological similarities between subcortical dementing syndromes and HIV-related cognitive impairment suggest that in both processes the pathogenesis of the observed deficits may involve disruption of frontodiencephalic projections.