A 51-year-old man presented with an extremely rare case of intracranial subarachnoid hemorrhage caused by rupture of an anterior spinal artery aneurysm manifesting as disturbance of consciousness following sudden onset of neck pain and numbness of the extremities. Cranial computed tomography revealed subarachnoid hemorrhage, mainly in the posterior fossa. Cerebral angiography studies on admission and on the 4th day demonstrated no definite abnormality as a bleeding source. A ventricular catheter was inserted to treat the acute hydrocephalus, and conservative management was continued during the acute period. Third angiography on the 18th day demonstrated an anterior spinal artery aneurysm at the C1 level which was considered to be the bleeding site. After conservative treatment, the patient was discharged without neurological deficits. Fourth angiography on the 108th day disclosed spontaneous disappearance of the aneurysm, which was confirmed by the fifth angiography on the 269th day. If subarachnoid hemorrhage of unknown etiology is encountered, spinal artery aneurysm should be considered as the bleeding source. Despite the controversy concerning the treatment strategy, ruptured spinal artery aneurysms can be treated conservatively because of the possibility of spontaneous regression. Follow-up angiography is required to evaluate the natural course of the lesion.