Hepatomegaly and liver dysfunction might develop in patients with diabetes mellitus due to glycogen deposition or nonalcoholic steatohepatitis. We experienced a case of hepatic glycogenosis in a patient with type 1 diabetes mellitus who presented with recurrent hypoglycemia, suggesting impairment of glycogenolysis and gluconeogenesis. A 10-year-old girl with a 4-year history of type 1 diabetes mellitus was admitted because of recurrent hypoglycemia and abdominal pain in the right upper quadrant. She had Cushingoid features and hepatomegaly that extended 6 cm below the right costal margin. Laboratory data and radiologic examination revealed elevated liver enzyme levels due to fatty liver. Periodic acid-Schiff (PAS) staining revealed intense glycogen deposition in the cytoplasm of the hepatocytes and PAS reactivity was lost with diastase treatment. At 2 months after administration of glucagon injection and uncooked cornstarch between meals and at bedtime, the hypoglycemic episodes and liver dysfunction improved. It is important to distinguish hepatic glycogenosis from steatohepatitis, because it is possible to prevent excessive hepatic glycogen storage in hepatic glycogenosis cases by strictly controlling blood glucose level and by glucagon administration. To prevent severe hypoglycemic symptoms accompanied by hepatic glycogenosis, we suggest that uncooked cornstarch, which is effective in maintaining blood glucose level, can also be administered.