Data from the Centers for Disease Control (CDC) and from the hospitals affiliated with the University of California, San Francisco show a significant incidence of neurological complications in AIDS patients and suggest that patients from different risk groups and geographic regions are at different relative risk for specific neurological complications. CDC national surveillance data show that Haitian-born AIDS patients are 3.7 times more likely to have neurological complications than are patients in other risk groups; neurological illness is also reported more often in intravenous drug abusers and black AIDS patients. Cryp-tococcal meningitis is most prevalent among intravenous drug abusers, Haitians, and blacks, and is most commonly reported in New Jersey, a state with a large proportion of AIDS patients in these three groups. Cerebral toxoplasmosis is reported much more often in Haitians than in other risk groups and is most prevalent in Florida among both Haitians and non-Haitians, probably because of greater exposure to Toxoplasma gondii organisms in the semitropical climate of Florida. The prevalence rates for progressive multifocal leukoencephalopathy (PML) and primary central nervous system lymphoma are similar throughout various risk groups and regions of the United States.