A retrospective study of 127 cases irradiated for glioblastoma was made to assess the role of radiation therapy and to determine the optimal technique of radiation therapy. The over-all survival rates of our series were 52 percent at one year, 19 percent at three years, and twelve percent at five years after radiation therapy. Survival time of the patients is influenced by various factors other than treatment: age, sex, histologic grading, duration of symptoms, and location of tumor. Among these factors, the location of the tumor was the most important in our present series. Surgical treatment can extend the survival time. More extensive resection results in longer survival, provided that the location of the tumor allows such a surgical procedure. Radiation therapy can prolong the survival time of those with glioblastoma, but a high tumor dose of more than 6,000 rads or 1,700 rets is necessary to improve the prognosis significantly. Therefore, irradiation should be administered through generous fields according to the extent of the tumor under precise planning to determine the accurate localization and extent of the tumor.