We report three cases of adult-onset type II citrullinemia (CTLN2) treated with different therapies including one case successfully treated with p.o. administration of sodium pyruvate and low-carbohydrate diet. Although recent advances in liver transplantation have enabled successful treatment of patients with CTLN2, several issues concerning liver transplantation remain. Further, there is still an urgent need for therapies that do not rely on liver transplantation. The first case was a 41-year-old man who developed impaired consciousness in 1992. The patient was treated with conventional therapy for hepatic encephalopathy and died of severe brain edema. The second case was a 31-year-old man who suddenly presented a syncope-like attack with hyperammonemia. He was treated with carbohydrate-restricted diet but the encephalopathy could not be controlled, and he received emergency living donor liver transplantation. The third patient was a 67-year-old man who developed abnormal behavior with hyperammonemia. He has remained well with oral sodium pyruvate and a low-carbohydrate diet without receiving liver transplantation.