To evaluate the efficacy and safety of intravenous cytarabine in the treatment of AIDS-associated progressive multifocal leukoencephalopathy (PML), we reviewed the charts of all human immunodeficiency virus-infected patients with PML who were seen during a 28-month period at our institution. Patients with biopsy-proven PML were offered therapy with intravenous cytarabine (2 mg/[kg.d] for 5 days every 4 weeks). The diagnosis of PML was histologically confirmed for 13 patients. The median CD4 cell count was 91 x 10(6)/L. A median of three courses of cytarabine was administered to eight patients. Two patients developed mild drug-related toxicities. Clinical and/or radiological signs of improvement were observed for three patients treated with cytarabine; no signs of improvement were noted for the untreated patients. Median survival time after the diagnosis of PML was 102 days (range, 46-220 days) for patients who received cytarabine and 60 days (range, 28-72 days) for untreated patients matched for Karnofsky scores (P = .06, logrank test). Although cytarabine is well tolerated by patients with AIDS and PML, only modest short-term clinical improvement in the conditions of patients treated with the drug has been observed, with no significant impact on survival.