A 32-year-old female complained of a headache persisting for approximately one week. She was emergently brought to the hospital for sudden consciousness disorder early in the morning. Her neurological state was JCS 200 and WFNS Grade V. CT scan demonstrated a subarachnoid hemorrhage. 3D-CTA and DSA showed a right true posterior communicating artery fusiform aneurysm. We performed open surgery the same day, and found that the aneurysmal wall had thinned markedly. The aneurysm ruptured, and trapping was performed. A perforating artery from the aneurysm was sacrificed, but there was no apparent neurological deficit. The patient was ambulatory when discharged after a VP shunt was implanted, and she has returned to normal daily life. True posterior communicating artery fusiform aneurysm is very rare, and has been reported in detail in only 6 cases to date. A brief clinical review of the literature is presented. Since this type of aneurysm enlarges rapidly in some patients, and the possibility of re-rupture in the acute period is high, prompt trapping after onset is recommended.