Obesity is a multifactorial, genetically-determined, neuroendocrine, and chronic condition. Conservative treatment of patients with class II and III obesity (BMI >35 kg/m(2)) has only modest long-term success. Surgical procedures have been used since 1954, and the methods used are continually being updated and improved. With experienced surgeons, patients can achieve a weight reduction from around 50% with purely restrictive procedures, increasing to 75% with combined restrictive-malabsorptive methods. All weight-loss methods offer a considerable improvement or elimination of obesity-related co-morbidities and substantially improvement of quality of life. Well-documented, long-term studies reveal a perioperative mortality of 0.2-1.0%, dependent on the surgeon's experience, and a maximum perioperative morbidity of 20%. Bariatric surgery is accepted as evidence based, safe and effective treatment of obesity.