A cerebral giant serpentine aneurysm (GSA) is a rare entity that is characterized by a partially thrombosed aneurysm measuring > 2.5 cm with a tortuous vascular channel [1]. Although numerous reports on this disease have been published, the mechanism underlying GSA formation remains unclear. Thus far, there have been no reports of GSA occurring after Gamma Knife radiosurgery (GKRS). This is a report on a case of a ruptured GSA of the anterior cerebral artery in a patient with a history of GKRS for arteriovenous malformation (AVM).