Obesity is endemic in the United States and is closely linked to the development of type 2 diabetes. Both obesity and diabetes are responsible for significant morbidity and mortality. Likewise, both conditions are resistant to treatment. Recent studies have evaluated prevention of type 2 diabetes through intensive lifestyle intervention, while others are examining the impact of bariatric surgery on type 2 diabetes. This article presents an overview of the impact of bariatric surgical and lifestyle interventions on the prevention and treatment of type 2 diabetes. Although studies using a variety of bariatric surgical techniques are included, the focus is on two interventions in particular: the Roux-en-Y gastric bypass and the laparoscopic silicone gastric banding procedure. Outcomes of these procedures are further contrasted with recent lifestyle intervention studies, in particular, the Diabetes Prevention Program study. Gastric bypass studies have been associated with a 99 to 100% prevention of diabetes in patients with IGT and an 80 to 90% clinical resolution of diagnosed early type 2 diabetes. Gastric banding procedures are associated with a lower median (50–60%) clinical remission of type 2 diabetes. Lifestyle intervention studies of obese and glucose-intolerant patients have achieved a 50% reduction in the progression of IGT to diabetes over the short term, with no reported resolution of the disease. Weight loss by any means in the obese patient appears to prevent progression to type 2 diabetes, at least in the short term. Furthermore, sustained weight loss through bariatric surgical intervention is associated both with prevention of progression of IGT and with clinical remission of early type 2 diabetes. Copyright © 2004 John Wiley & Sons, Ltd.