Overweight and obesity are the most common metabolic disorders affecting the U.S. with 31% of adults and 16% of adolescents now meeting Centers for Disease Control criteria for these conditions. As the obesity epidemic has unfolded, so too has the increase in prevalence of abnormalities of carbohydrate metabolism. The single most effective treatment for type 2 diabetes in severely obese adults may be bariatric surgery, a procedure that is most commonly performed in the 5th and 6th decades of life. While it is clear that rapid and profound weight loss can significantly improve carbohydrate metabolism in adults, it is not clear to what degree type 2 diabetes is reversible in these patients. The pathophysiology of type 2 diabetes in adolescents and children is not well understood and no studies have yet examined the effect of surgical weight loss on insulin resistance, insulin secretion, or glucose tolerance in severely obese young people. However, it seems likely that bariatric surgery could improve these conditions in youth. Understanding the relative benefits of surgically induced weight reduction on carbohydrate metabolism in adolescents compared to older subjects is important for determining optimal timing of this intervention. This knowledge may also lead to key insights into obesity-induced diabetes. In this project we will test the hypothesis that bariatric surgical intervention will more effectively improve insulin resistance, β cell dysfunction, and glucose tolerance in adolescents compared to adults. Three specific aims are proposed: 1) To compare the derangements of carbohydrate metabolism among very severely obese (body mass index ≥ 40 kg/m2) adolescents and adults referred for bariatric surgery; 2) To assess improvement in carbohydrate metabolism longitudinally (during and after surgical weight loss) comparing differences in the mechanisms of improvement between the two age groups; 3) To compare major complications in the two age groups following bariatric surgery. These data will provide critical information about age-related metabolic outcomes of bariatric surgery and could inform the design of larger studies to examine the role of early bariatric surgery in management of disorders related to insulin resistance in patients at high risk for these conditions.