Brain involvement in small cell carcinoma of the lung is a common phenomenon occurring in from 29 to 45% of patients. Because of this, it was suggested that prophylactic brain irradiation be made a part of treatment plans for small cell carcinoma. In December 1974, the Southwest Oncology Group (SWOG) began treating patients with combination chemotherapy and irradiation of both the primary lesion and whole brain. In two years, there were 390 patients entered into the study. In patients with extensive disease only 6 of 152 prophylactically irradiated patients developed CNS signs or symptoms of CNS recurrence. In limited disease, 6 of 88 prophylactically treated patients had CNS recurrence and in only 4 was this the site of initial failure. We feel prophylactic brain irradiation in small cell carcinoma of the lung is of benefit.