Ten immunocompetent patients with primary non-Hodgkin's lymphoma of the central nervous system were treated by the neuro-oncology service at the University of California at San Francisco (UCSF). After undergoing surgery for biopsy or removal of their tumors, these patients (group 1) received irradiation with hydroxyurea followed by adjuvant chemotherapy with the combination of procarbazine, lomustine (CCNU), and vincristine. The outcome of treatment in this group was compared with that in three other groups of patients with primary CNS lymphoma: patients treated at the UCSF Cancer Research Institute who underwent surgery and radiation therapy (RT) (group 2); patients described in the literature who had surgery and RT (group 3); or patients described in the literature who had surgery, RT, and chemotherapy (group 4). Median and quartile survival times were greater in patients who received adjuvant chemotherapy (group 1, 30 and 50 months; group 4, 20 and 25 months) than in patients who did not receive chemotherapy after RT (group 2, 13 and 20 months; group 3, 15 and 24 months). These results suggest that adjuvant chemotherapy is useful in the treatment of primary CNS lymphoma.