A case of glycogen disease of the liver (von Gierke's disease), followed from the age of 6 months to death at 10½ years, is reported. The child was dwarfed and mentally retarded. The diagnosis is supported by blood sugar concentrations following the administration of monosaccharides and following epinephrine injection as well as by post-mortem anatomical and chemical studies. Hypoglycemia was controlled by frequent feedings which contained glucose or starch. Levulose and galactose were restricted because low tolerance tests suggested that these substances were rapidly removed from the blood by the liver; after phosphorylation and conversion in the liver their release as glucose was evidently blocked by the same mechanism that blocked the release of glucose from glycogen. Blood lactic acid was consistently elevated, the degree of elevation bearing an inverse relationship to blood sugar levels. It is suggested that excess blood lactic acid contributes to the acidosis and so therapy of the acidosis with lactates would be illogical. The concentration of total serum lipids was always high but fluctuated widely, reaching a peak of 7.45 gm./100 ml., higher during periods of prolonged hypoglycemia and probably reflecting the mobilization of body fat during these periods. The terminal illness was marked by 2 unexplained complications: multiple hepatomata and congestive right heart failure. The severity of the disease varies from patient to patient, in the present case appearing to decrease with advancing age.