PURPOSE: Conventional therapy--ie, treatment with corticosteroids and cranial radiotherapy (RT)--is inadequate to treat AIDS-related primary central nervous system lymphoma (PCNSL), as it achieves a median survival of only 2 to 5 months. Chemotherapy added to RT in non-AIDS PCNSL improves disease control and prolongs survival. We studied the efficacy of this approach with RT in AIDS-related PCNSL. METHODS: Ten AIDS patients with PCNSL were treated with chemotherapy--nine at diagnosis and one at recurrence. None had evidence of systemic lymphoma. All patients treated at diagnosis received pre-RT methotrexate--eight also received thiotepa and procarbazine--followed by whole-brain RT. The patient treated at recurrence (who had been previously irradiated) received chemotherapy alone, including methotrexate, thiotepa, and procarbazine. RESULTS: All had enhancing lesions on MRI and five (50%) had a single lesion (seven [70%] had a ring-enhancing mass). No patient had a response to corticosteroids. Four of seven (57%) assessable patients had a partial or complete response to chemotherapy prior to RT. Six of seven (86%) assessable patients had a complete response at the end of treatment. Median survival was 3.5 months for all 10 patients and 7 months for the eight patients who completed therapy. Two patients survived for 1 year or longer. Eight patients died--six from infection (two treatment-related), one from progressive dementia, and one from a gastrointestinal hemorrhage. CONCLUSION: AIDS-related PCNSL responds to chemotherapy and RT, but only a few patients benefit with prolonged survival.