Primary malignant lymphoma of the brain (PMLB) is uncommon. Between 1975 and 1982, the authors observed 11 patients with histologically confirmed PMLB. Mean survival after radiation therapy was 7 months with 5 patients surviving for more than 2 years. Multifocal lesions were seen in 9 patients and spontaneous regression was seen at computed tomography in 2 patients. Radiation doses in excess of 30 Gy controlled the primary tumor, but intracranial recurrences occurred even after whole brain irradiation to 40 Gy. Only one patient had a relapse outside the central nervous system, and none had clinical evidence of seeding to the spinal canal. The authors postulate that PMLB usually is a multifocal intracranial disease, and that whole brain irradiation of at least 30 to 40 Gy should be given to all patients with this disease.