A 34-year-old female presented with occlusive cerebrovasculopathy without definite ischemic symptoms and regrowth of a cystic tumor in the third ventricle. She had been treated for a craniopharyngioma 19 years previously by internal irradiation with ¹⁹⁸Au colloid combined with intracavitary administration of bleomycin via an Ommaya reservoir. Cerebral angiography demonstrated complete occlusion of the clinoid portion of the left internal carotid artery and stenosis of the left posterior cerebral artery, and numerous transdural anastomoses which had developed after craniotomy. Endoscopic management achieved collapse of the cystic tumor. No treatment for the occlusive cerebrovasculopathy was necessary because of the collateral blood supply. Careful follow-up examinations to detect occult cerebrovasculopathy after such treatment is recommended.