In this retrospective study from five centres, 139 patients over 10 years of age with glycogen storage disease types I, III, VI and IX are described. Almost half of the patients with glycogen storage disease type Ia had retarded growth and most had hyperlipidaemia. One-third of the patients had adenomas, although none of these showed malignant transformations. With increasing age the growth, liver size and hyperlipidaemia of patients with glycogen storage disease type III improve. However, there was a high incidence of myopathy and cardiomyopathy. Patients with glycogen storage disease types VI and IX had a normal growth pattern after childhood. Hepatomegaly and hypercholesterolaemia, however, were still present in half of the patients.