We report herein a case of a radiation-induced aneurysm. A 69-year-old woman presented with subarachnoid hemorrhage. Eight years previously, she had undergone cranial radiation therapy (total dose of 59.4 Gy) as adjuvant therapy after surgical resection for a chondrosarcoma that was destroying her sphenoid sinus. The patient underwent catheter angiography, which revealed an aneurysm of the anterior communicating artery and luminal narrowing and irregularity in the petrous and lacerum segments of the right internal carotid artery. We attempted surgical clipping of the aneurysm, but there was repeated bleeding. Finally the aneurysm was treated with endovascular trapping. Potentially fatal bleeding also occurred from her internal carotid artery, which had also been irradiated during the previous cranial radiation therapy. We stopped the bleeding with endovascular coil embolization. Because of diffuse vascular changes of the cerebral vessels within irradiated fields, special attention must be paid to their treatment.