Late radiation brain injury after treatment for pituitary adenomas was analyzed retrospectively. From 1970 to 1983, 53 patients with pituitary adenomas were treated at our clinic with postoperative radiation therapy (RT) or RT alone. During the period under study, patients were treated with various fractionation schedules. Initially, each fraction size was 2-2.5Gy, 5 days per week for a total delivered dose of 50-60Gy. Later the fraction size was changed to 3Gy, 3 days per week, for a total dose of 51-60Gy, to increase the rate of control of the tumor. The field size ranged from 9cm² to 40cm², and parallel opposed portals were used. Radiation brain injury was diagnosed clinically and radiographically with CT, ²⁰¹T1-SPECT, ¹⁸FDG-PET. Radiation brain injury occured in 6 patients (1 patient had reversible injury, and the others had irreversible injury). Irreversible radiation injury occurred in patients who received more than 51Gy at 3Gy per fraction (51Gy, 1 case; 60 Gy, 2 cases), but did not occur in patients who received 50-60Gy at 2-2.5Gy per fraction. The case with irreversible injury who received 51Gy had severe complications after surgery, and that was suspected to be one of the causes of the injury. There was no relation between field size and radiation injury. We conclude that, radiation doses of 60Gy at 3 Gy per fraction do not seem to have any therapeutic advantage.