Besides genetic predisposition, obesity is the most important risk factor for the development of diabetes mellitus, and weight reduction has been shown to markedly improve blood glucose control in obese subjects with type 2 diabetes. Therapeutic strategies for the obese diabetic patient include: 1) promoting weight loss through lifestyle modifications (hypocaloric diet and exercise) and anti-obesity drugs (orlistat, sibutramine, etc.); 2) improving blood glucose control, essentially through the reduction of insulin resistance (metformin, eventually thiazolidinediones) or insulin need (α-glucosidase inhibitors) and, at a later stage, the correction of defective insulin secretion (sulphonylureas, repaglinide) or low circulating insulin levels (exogenous insulin); and 3) treating common associated risk factors, such as arterial hypertension and dyslipidaemias, to improve cardiovascular prognosis. When morbid obesity is present, both restoring a good glycemic control and correcting associated risk factors can only be obtained through marked and sustained weight loss. This primary objective justifies more aggressive weight reduction programmes, including very low-caloric diets and bariatric surgery, but only within a multidisciplinary approach and in well-selected patients.