A 78-year-old woman underwent magnetic resonance (MR) imaging to assess the deterioration of her right hemiparesis initially caused by putaminal hemorrhage that occurred 5 years prior to referral. MR imaging detected an anterior communicating artery aneurysm but no new lesion was seen that might have caused the deterioration was observed. Hemiparesis improved within several days and she was referred for endovascular treatment of the aneurysm. Digital subtraction angiography demonstrated a 4.4 mm long aneurysm at the A1-A2 junction of her left anterior cerebral artery. Information on the risk associated with treatment caused her to hesitate. Three days after discharge and 40 days after the discovery of the aneurysm it ruptured, causing severe subarachnoid hemorrhage. The patient died on the following day.