Radiotherapy is a standard postoperative treatment for various cerebral neoplasms. Howewr, radiation has the potential to produce severe injury to normal brain tissue in and around the tumor bed. The authors encountered 7 patients with delayed cerebral necrosis. These unacceptable complication prompted us to analyze cases with such a complication particularly in regard to the differential diagnosis between the recurrence of the tumor and radiation necrosis of the brain. This article summarizes factors related to the radiation necrosis, including clinical observations and treatment.