Primary central nervous system lymphoma in patients with and without the acquired immune deficiency syndrome. A retrospective analysis and review of the literature. Twenty-two cases of PCL were reviewed, in which 9 patients had AIDS and 13 did not. A review of the literature identified 247 cases of AIDS-related PCL. Differences between patients with AIDS and immunocompetent PCL were noted in our series. AIDS-related PCL when compared to non-AIDS PCL in our series has the following notable clinical features: 1) significantly younger age at presentation, median age 34 versus 59 years; 2) significantly higher incidence of B symptoms, 44% versus 8%; 3) worse median performance status at presentation, 3 versus 1; and, 4) shorter median survival, 3 versus 10 months. Differences in performance status and survival, however, were not significant. AIDS-related PCL is further characterized by frequent (44%) ring-enhancing mass lesions on head CT scan, a finding that makes it clinically difficult to distinguish from toxoplasmosis. Median survival appears to be improved in the absence of opportunistic infection at time of diagnosis of PCL, 6 versus 2 months. The therapeutic approach to patients with PCL, with and without AIDS, is variable. Combined modality therapy may improve the survival in patients with non-AIDS PCL. Therapy for patients with AIDS-related PCL is tailored to the status of the individual and it is, therefore, difficult to make comparisons to non-AIDS PCL patients. AIDS patients are often too ill to tolerate aggressive surgery or systemic treatment and in this instance, radiotherapy alone may be an acceptable alternative. Nonetheless, overall survival for patients with AIDS-related and non-AIDS PCL remains poor. 