Two rare cases of fusiform aneurysms of A1 segment of the anterior cerebral artery are reported. Case 1: A 62-year-old woman was admitted with sudden onset of severe headache and loss of consciousness, on August 22, 1982. CT scan showed subarachnoid hemorrhage at the basal cisterns. Left carotid angiography revealed a spindle shaped aneurysmal dilatation in the A1 segment of the anterior cerebral artery. Four-vessel angiography was performed twice but no other aneurysm was found. She was treated conservatively and the clinical course was not eventful. She was discharged with no neurological deficit one month after the admission. Case 2: A 49-year-old man complained of sudden onset of severe headache, nausea and vomiting on August 24, 1986. He was transferred to a local hospital and CT scan showed subarachnoid hemorrhage at the basal cisterns. Angiography revealed a fusiform aneurysm of the proximal anterior cerebral artery. He was referred to our hospital on the day of onset. He was operated on via bifrontal interhemispheric approach. The fusiform aneurysm of A1 segment was trapped successfully using temporary occlusion of A1 and A2 bilaterally under the administration of Sendai-Cocktail. V-P shunt was performed 1 week after the aneurysmal operation. The post-operative course was uneventful. He was discharged with no neurological deficit three months after operation. As far as we know, there are 6 cases of fusiform aneurysm of A1 segment of anterior cerebral artery in the literature. In this report, our two cases were described and treatment of such aneurysms were discussed.