Of 77 patients with supratentorial Grades I and II astrocytoma diagnosed from January 1975 to December 1984, 66 were treated with postoperative radiation therapy. The patients received a tumor dose of 5000 to 5500 cGy in 180 cGy fractions, five fractions per week, over 5.5 to 6 weeks. Overall actuarial survival at 2, 5, and 10 years was 71%, 55%, and 43%, respectively. Progression-free survival at 2, 5, and 10 years was 69%, 50%, and 39%, respectively. Survival for patients receiving postoperative radiation therapy in the range of 4500 to 5900 cGy was 78% and 66% at 2 and 5 years, respectively. Quality of life was determined at two points in time: 1 to 2 years postoperatively, and at last follow-up (2-12 years postoperatively). The occurrence of mental retardation was specifically addressed in long-term survivors, and was observed in 50% of children. Overall, however, 80% of short-term survivors and 67% of long-term survivors were intellectually and physically intact, without major neurologic deficit. Specific prognostic factors were assessed by multivariate analysis. Improved survival was observed with young patients, females, normal preoperative mental status, surgical resection (versus biopsy alone), involvement of only one lobe with tumor, and a history of preoperative seizures. A weighted prognostic factor score derived from these observations permits a clinically useful assessment of risk for individual patients.