The purpose of this study was to determine the nature and extent of neuropsychological abnormalities among HIV-infected individuals and to examine the interrelationships between measures of cognitive functions and the factors that predict neuropsychological abnormalities. The study focused on cross-sectional data gathered in a multidisciplinary research clinic form 200 HIV-infected (HIV +) men and women recruited from primary medical care settings. Composite scores representing six cognitive domains were derived from the neuropsychological test data. Scores of memory, fluency, spatial, and frontal functions could be predicted by independent assessment of participants' verbal and psychomotor speed abilities. Basic verbal ability itself was predicted by education, race, and handedness, whereas speed was predicted by age, CD4+ cell counts, and a lifetime history of major depression. This model of effects is consistent with the hypothesis that psychomotor slowing is central to mild cognitive disorder in HIV infection and that such changes are associated with markers of the severity of systemic infection.