RESUMEN
Morbid obesity is defined as obesity with body mass index (BMI) > or = 40 kg/m2 with secondary serious diseases. Conservative treatment generally fails to produce long-term weight loss in these patients, since several bariatric surgical techniques have been developed which are based on gastric restriction and/or gastric malabsorption resulting in permanent weight loss over years. Preoperative evaluation might detect suitable patients and reduce both non-surgical and surgical complications. Postoperative follow-up in a multidisciplinary program, including specialists in various fields of medicine, e.g. surgery, internal medicine, radiology, paediatrics and nutritional surveillance are mandatory in the treatment of patients after obesity surgery. Bariatric surgery results in a major weight loss, with amelioration of most obesity-associated conditions. The most serious side effect of some surgical procedere is malnutrition.