BACKGROUND: The increasing prevalence of morbid obesity together with the development of laparoscopic approaches has led to a steep rise in the number of bariatric operations. These guidelines intend to define the comparative effectiveness and surrounding circumstances of the various types of obesity surgery. METHODS: A consensus panel representing the fields of general/endoscopic surgery, nutrition and epidemiology convened to agree on specific questions in obesity surgery. Databases were systematically searched for clinical trial results in order to produce evidence-based recommendations. Following two days of discussion by the experts and a plenary discussion, the final statements were issued. RECOMMENDATIONS: After the patient's multidisciplinary evaluation, obesity surgery should be considered in adults with a documented BMI greater than or equal to 35 and related comorbidity, or a BMI of at least 40. In addition to standard laboratory testing, chest radiography, electrocardiography, spirometry, and abdominal ultrasonography, the preoperative evaluation of obesity surgery patients also includes upper gastrointestinal endoscopy or radiologic evaluation with a barium meal. Psychiatric consultation and polysomnography can safely be restricted to patients with clinical symptoms on preoperative screening. Adjustable gastric banding (GB), vertical banded gastroplasty (VBG), Roux-en-Y gastric bypass (RYGB) and biliopancreatic diversion (BPD) are all effective in the treatment of morbid obesity, but differ in degree of weight loss and range of complications. The choice of procedure therefore should be tailored to the individual situation. There is evidence that a laparoscopic approach is advantageous for LAGB, VBG, and GB (and probably also for BPD). Antibiotic and antithromboembolic prophylaxis should be used routinely. Patients should be seen 3 to 8 times during the first postoperative year, 1 to 4 times during the second year and once or twice a year thereafter. Outcome assessment after surgery should include weight loss and maintainance, nutritional status, comorbidities and quality-of-life.