Severe hypoglycemia is an important but uncommon complication of anorexia nervosa. A 35-year-old woman showed severe hypoglycemia after a recovery from severe liver dysfunction due to malnutrition.To reveal the cause of severe hypoglycemia, we measured plasma hormones and performed a 75g oral glucose loading test.Fasting serum adrenocorticotropic hormone, cortisol, growth hormone, somatostatin, and active ghrelin were elevated. Serum free triiodothyronine, leptin, and adiponectin were reduced. Plasma glucose fluctuated from 67 to 76 mg/dl after a 75g glucose ingestion, without hyperinsulinemia. Serum growth hormone, somatostatin, and active ghrelin levels were decreased after glucose ingestion. Plasma glucagon levels were increased and remained at high levels at 120 min, and glucose-dependent insulinotropic polypeptide (GIP) levels were continuously and remarkably increased after glucose ingestion.We observed a strongly reduced sensitivity in glucagon-induced hepatic glycogenolysis, and significantly elevated fasting and postprandial GIP levels, and a defective GIP-mediated glucagon secretion, in an anorectic patient with severe hypoglycemia.