We reviewed 24 children who had symptomatic gliomas that involved the optic chiasm and were treated with definitive radiation therapy from 1971 to 1986. In eight patients (33%), histologic confirmation of low-grade astrocytoma was obtained. Patients had radiation therapy only if there was evidence of visual deterioration or other clinical or radiographic evidence of disease progression. Radiation doses ranged from 4500 to 5660 cGy (median, 5400 cGy) with up to a 17-year follow-up period (median, 6 years). The 6-year actuarial freedom from disease progression and overall 6-year survival are 88% and 100%, respectively. Visual improvement or stabilization was seen in 21 (91%) patients after radiation. A high incidence of endocrine abnormalities is reported, with 15 of the 18 patients evaluated after treatment showing growth hormone deficiency. We conclude that definitive radiation therapy is associated with tumor control in most of the patients with progressive optic chiasm gliomas. However, neuropsychiatric and endocrine abnormalities are significant problems that need additional evaluation in these children.