As part of a longitudinal study, 265 cerebrospinal fluid (CSF) specimens from 204 human immunodeficiency virus type 1 (HIV-1)-seropositive subjects and 43 seronegative controls were evaluated. Of the 204 seropositive persons, 78 (38%) had > or = 1 CSF culture positive for HIV-1; the probability of being culture positive increased as the number of CSF samples obtained increased (P = .0018). Significantly correlated with culture positivity were elevations in CSF protein level (P = .014) and CSF white blood cell count (P = .001). Virus was more readily cultured from clarified CSF (89%, 42/47) than from the cellular fraction (30%, 14/47; P < .00001). Amplification of HIV-1 DNA by polymerase chain reaction (PCR) from 25 seropositive persons was positive in 9 (82%) of 11 culture-positive and in 4 (29%) of 14 culture-negative specimens, while amplification of viral RNA detected all 11 culture-positive and 9 (64%) of the 14 culture-negative CSF specimens. These data support the hypothesis that the development of HIV-1-associated neurocognitive disorders are not dependent solely on the presence of HIV-1 within the central nervous system.