An 18 year-old woman received radiation therapy for hypothalamic astrocytoma at the age of 11 years. She developed progressive cerebral occlusive vascular disease with moyamoya vessels formation in both carotid systems. Apart from diabetes mellitus, she had no other risk factors for occlusive cerebrovascular disease. The site of occlusion was confined to the field of radiation and the development of moyamoya vessels strongly suggestive of a radiation-induced cause. Radiation therapy around the sella and parasellar region appears to be the most common risk factor for this vasculopathy. Progressive irradiation-induced cerebral vasculopathy is due to accelerated atherosclerosis.