Type Ia glycogen storage disease, or von Gierke Disease (MIM 232200), is caused by a deficiency of glucose 6-phosphatase activity in the liver, kidney, and intestinal mucosa, with excessive accumulation of glycogen in these organs. The stored materials in the liver include both glycogen and fat. The clinical manifestations are growth retardation, hepatomegaly, hypoglycemia, lactic acidemia, hyperuricemia, and hyperlipidemia. A variant caused by a defect in the transport of glucose 6-phosphate (type Ib) (MIM 232200) has the additional findings of neutropenia and impaired neutrophil function, resulting in recurrent bacterial infections and oral and intestinal mucosa ulceration. Both type Ia and Ib genes have been cloned and mutations responsible for the diseases identified. In the past, many patients with type I glycogen storage disease died, and the prognosis was guarded in those who survived. Long-term complications include gout, hepatic adenomas, osteoporosis, renal disease, and short stature. Major progress has been made in managing this disorder. The current treatment of type I glycogen storage disease is nocturnal nasogastric infusion of glucose or orally administered uncooked cornstarch. Both methods are effectively improving growth, reducing hepatomegaly and sustaining the commonly measured metabolic indexes of adequate therapy in patients with type I glycogen storage disease. Early diagnosis and early initiation of an effective treatment have improved the outcome of the disease, but it is not known if all long-term complications can be avoided by good metabolic control. Some early treated patients who are now adults still develop hepatic adenomas and proteinuria.