AIDS dementia complex is a common neurologic disorder in later stages of HIV-1 infection. Because virus-specific CTL have been shown to contribute to neurologic disease in certain viral illnesses, we examined the cerebrospinal fluid of HIV-1-infected persons with various stages of AIDS dementia complex for the presence of HIV-1-specific CTL. In five of six subjects studied, HIV-1-specific CTL were identified in the cerebrospinal fluid. These CTL were directed at epitopes within the gag, reverse transcriptase, envelope, and nef proteins and restricted by HLA class I Ag. In four of these subjects, virus-specific CTL were detected in higher numbers in the cerebrospinal fluid compared to the peripheral blood, suggesting a specific recruitment to or local induction within the nervous system. These studies demonstrate the presence of a vigorous and broadly directed CTL response to HIV-1 in the central nervous system of infected persons with AIDS dementia complex, and provide immunologic evidence of localized intrathecal infection. Although HIV-1-specific CTL may serve to inhibit viral replication in the central nervous system, the presence of a persistent CTL response in the central nervous system may also contribute to the neurologic disorders characteristic of HIV-1 infection.