A multicenter analysis of 57 consecutive human immunodeficiency virus-positive patients with progressive multifocal leukoencephalopathy (PML) was performed, to identify correlates of longer survival. JC virus (JCV) DNA was quantified in the cerebrospinal fluid (CSF) by polymerase chain reaction. Two months after therapy, 4% of the patients without highly active antiretroviral therapy (HAART) and 26% with HAART showed neurologic improvement or stability (P=.03), and 8% and 57%, respectively, reached undetectable JCV DNA levels in the CSF (P=.04). One-year probability of survival was.04 without HAART and.46 with HAART. HAART and lack of neurologic progression 2 months after diagnosis were independently associated with longer survival. Among HAART-treated patients, a baseline JCV DNA <4.7 log, and reaching undetectable levels after therapy predicted longer survival. Survival of AIDS-related PML is improved by HAART when JCV replication is controlled.