A 42-year-old man presented with a ruptured fusiform aneurysm of the proximal anterior cerebral artery (A(1) segment) manifesting as sudden onset of severe headache. Brain computed tomography revealed subarachnoid hemorrhage in the basal cisterns, and left carotid angiography demonstrated a fusiform aneurysm of the left A(1) segment. He underwent surgery via the left pterional approach. The left A(1) segment exhibited a fusiform configuration. Adequate development of the anterior communicating artery was confirmed. Trapping of the aneurysm was performed. The aneurysm was associated with atherosclerotic changes. The postoperative course was uneventful, and the patient was discharged without neurological deficits 1 month after surgery. Fusiform aneurysm of the A(1) segment is quite rare, and tends to bleed, so must be treated. The atherosclerotic origin indicates long-term follow up to identify subsequent lesions.