CT findings and the results of radiotherapy were retrospectively evaluated on 11 patients with primary malignant lymphoma of the brain treated at UOEH Hospital from November, 1979 to March, 1989. CT mostly showed an isodensity or slightly high-density round masses with marked contrast enhancement and was useful both for an initial diagnosis and an evaluation of the response following treatment. Radiation therapy was given to the whole brain in 9 patients. Two patients were irradiated only locally to the tumor bearing area, but no long-term effect was observed. The total dosage ranged from 30 to 51.2 Gy. The 8 patients who received 50 Gy or more to the tumors had higher survival and local control rates than the other 3 who received less than 40 Gy. We conclude that whole brain irradiation with at least a total dose of 50 Gy to the tumor area is necessary to control malignant lymphoma of the brain.