A polymerase chain reaction (PCR)-based method was used to detect cytomegalovirus (CMV) DNA in 82 cerebrospinal fluid (CSF) samples from 67 patients infected by human immunodeficiency virus (HIV). The test was positive for 14 patients, 8 of whom had CMV-related neurologic disease proven by viral culture of CSF or histologic examination. Encephalitis was the most frequent manifestation in patients with positive PCR results, but CMV DNA was also present in some patients with peripheral neuropathy or polyradiculomyelitis. All patients with proven CMV neurologic disease were positive by PCR. In contrast, viral culture was negative for 4 of the 8 patients and pathologic studies were available only for 5. The specificity of the PCR-based assay could not be assessed precisely because of the lack of a reference standard, but the results correlated well with clinical course and results of the other methods. These findings suggest that the PCR-based method may be a useful noninvasive tool for the rapid diagnosis of CMV-related neurologic disease.