The long-term results of bariatric surgery are usually significantly better than those achieved with conventional management. The greatest benefits offered by bariatric surgery include a reduction in obesity-related diseases and a perceived improvement in the quality of life. Gastric bypass is the most commonly performed operation for weight loss. Surgery may be considered as a treatment option for patients with a body mass index (BMI) greater than 40 kg/m2, provided that the patient has precedingly participated in a weight management group programme with success (weight loss > 7%). Surgery may also be considered for patients with a BMI of 35-40 kg/m2 when obesity is associated with pharmacologically treated type 2 diabetes or hypertension, severe sleep apnoea (CPAP therapy) or severe disease of the musculoskeletal system.