Metabolic surgery is becoming an impressive therapeutic option for type 2 diabetes mellitus and other metabolic diseases. Compared to conservative therapy bariatric procedures, such as gastric bypass, sleeve gastrectomy, gastric banding and biliopancreatic diversion, seem to achieve significantly higher remission rates and improvements in blood glucose metabolism. Recent studies describe additional effect mechanisms which go beyond the assumed mechanisms of restriction and malabsorption. The results in the current literature suggest that gastric bypass and sleeve gastrectomy provide the best metabolic risk-benefit profiles. Gastric banding and biliopancreatic diversion can only be recommended in specific cases.