The relationship between the presence and severity of AIDS dementia complex (ADC) and the levels of human immunodeficiency virus type 1 (HIV-1) RNA in cerebrospinal fluid (CSF) were assessed. Nineteen patients with ADC (stages 1-3), 6 without ADC (group 1), and 10 (group 2) without ADC but with cryptococcal meningitis or progressive multifocal leukoencephalopathy were studied. There was a significant relationship between increasing CSF virus burden and ADC severity (P=.0006) but not with plasma burden and ADC severity. In group 2, CSF HIV-1 RNA levels in patients with cryptococcal meningitis were elevated. These results show that CSF HIV-1 RNA concentrations correlate well with ADC severity but may also be increased by central nervous system infections, such as cryptococcal meningitis.