OBJECTIVE: Although there is evidence of increasing prevalence of impaired glucose metabolism in obese children from smaller single cohorts, data are lacking on the progression of glucose metabolism in this patient group.We aimed to assess the prevalence and the longitudinal course of impaired glucose metabolism assessed by oral glucose tolerance test (oGTT) in a large multi-center pediatric obesity registry. SUBJECTS: We performed an observational multicenter (n=84) cross-sectional (n=11 156) and longitudinal analysis (n=1008) on the course of glucose metabolism evaluated by oGTT in obese children documented in the Adiposity Patients Verlaufsbeobachtung (APV) registry. Patients were stratified with impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and Type 2 diabetes (T2D), according to American Diabetes Association criteria. RESULTS: A total of 12.6% of the children presented with abnormal glucose metabolism (5.99% IFG, 5.51% IGT, 1.07% T2D). Body mass index (BMI) correlated modestly with 2-h blood glucose (r=0.04, P<0.001).In the 1008 patients with follow-up oGTT, metabolic parameters improved and the percentage of abnormal glucose metabolism decreased from 18.7 to 14.2%. Of the children with initial IGT, 70.6% converted to normal glucose tolerance. The improvement in oGTT results was associated with, but not dependent on, a reduction of BMI s.d. score. CONCLUSION: In summary, we provide evidence for significant improvement of oGTT parameters in obese children treated in specialized treatment centers, even though reduction in BMI was modest.