A 58-year-old woman was admitted to our department due to headache. Brain computed tomography [CT] indicated subarachnoid hemorrhage [SAH], and emergency angiography showed dissecting aneurysm involving the left A1 segment We performed trapping of dissecting A1 aneurysm and the postoperative course was uneventful. We present a case of dissecting aneurysm in the anterior cerebral artery with spontaneous SAH which was treated by early surgery and resulted in clinically good prognosis.