A 65-year-old woman presented with subarachnoid hemorrhage (SAH). Angiography detected a small bulge in the A1 segment of the right anterior cerebral artery (ACA). The patient was managed conservatively. Ten days after the initial SAH, the patient suffered a second SAH. Cerebral angiography demonstrated a fusiform aneurysm in the right A1 segment and vasospasm in the left A1 segment. The aneurysm of the right A1 segment was trapped and the right superficial temporal artery (STA) was end-to-end anastomosed to the distal portion of the right A1 segment. The patient had no postoperative cerebral ischemic events. Postoperative cerebral angiography revealed that the bypass flow through the right STA perfused the right ACA territories. STA-A1 end-to-end anastomosis can prevent cerebral ischemic events following parent vessel occlusion or microsurgical trapping for fusiform cerebral aneurysms in the A1 segment without sufficient collateral flow to the ipsilateral ACA territory from the contralateral ACA.