We report a 17-year-old female case of ornithine transcarbamylase (OTC) deficiency who died of brain edema due to hyperammonemic attack. The patient had a brother with OTC deficiency who had died of hyperammonemia at 17 years of age. She firstly had a symptom of headache, nausea, vomiting and myalgia at 14 years old and twice thereafter. On admission she had a severe disorientation and vomiting. The plasma ammonia level was 89 micrograms/dl, then increased to 400 micrograms/dl in five hours. In addition to plasma exchange, hemodialysis and then peritoneal dialysis for next 5 days, parenteral sodium benzoate and arginine were administered. Although the plasma ammonia level improved gradually, her consciousness never returned and she died of severe brain edema with uncontrollable hypotension on day 8. Histology of a necropsy liver sample showed fatty metamorphosis of hepatocytes mainly with fine lipid droplets. Electron micrograph of hepatocytes showed crystalloid inclusions in mitochondria. Significance of the clinical course and the treatment during hyperammonemic crisis was discussed.