The authors report below a clinical study of 23 patients bearing 31 primary central nervous system lymphomas diagnosed between January 1985 and December 1994. The cohort included 13 men and 10 women whose mean age was 46 years, ranging from 28 to 61 years. No patient had antecedent of human immunodeficiency virus positivity but one had a past history of rheumatoid arthritis. The duration of symptom was less than 8 weeks in 52% of the patients. Symptom groups included increased intracranial pressure(78%), focal neurological decificit(52%), neuropsychiatric symptoms(43%), and seizures(13%). The histopathologcal diagnosies were done in 19 cases(10 cases by resective surgery, 9 cases by open or stereotactic biopsy). The others were diagnosed by the typical clinical course such as rapid disappearance of lesions after steroid therapy, and/or radiological findings. Histological subtypes(National Cancer Institute Working Formulation) was confirmed in 8 patients including 3 cases of diffuse larger cell type. Phenotype was determined in 7 patients: 4 were B-cell type and 3 were T-cell type. One patient committed suicide during the radiation therapy and was therefore excluded from the survival analysis. All but two patients received radiation therapy. Five patients received chemotherapy. The over-all Kaplan-Meier survival rate was 46% at 2 years and 15.5% at 5 years. On univariate analysis, statistically significant prognostic factor associated with survival was not found but the higher Karnofsky score and single lesion were found to be favorable to the long-term survival. In the statistical analysis of the patients who received radiation therapy, surgical resection did not significantly influence the survival.