The clinical syndrome of hyperammonemic encephalopathy is often encountered in the context of decompensated liver disease. Although it is rare in patients without hepatic disease, non-hepatic causes cannot be excluded. Anesthesiologists should be careful in choosing the anesthetic agent and perioperative management for hyperammonemic patients in order to avoid acute hyperammonemia and encephalopathy. We report successful general anesthesia during GDC (Guglielmi detachable coil) embolization for a large unruptured aneurysm in the right distal internal carotid artery in a female patient with hyperammonemic encephalopathy that was caused by a portal-systemic shunt.