After bariatric surgery there are some favourable effects on comorbidities of obesity as glucose and lipid metabolism besides weight loss. Therefore surgical measures targeting at improvement of such metabolic disorders especially diabetes type 2 has been called "metabolic surgery". The complexity of its underlying metabolic mechanisms is not yet clear, but restriction of energy and weight loss (maintenance) seem to be the cornerstones.Risks of these procedures which are drawn of the established methods of bariatric surgery are reported to be relatively low in qualified centers. Being an elective operation special focus has to be set on mortality and morbidity, numbers of therapeutic failure and redo-surgery. Multiple irreversible and not seldom severe, potentially life-threatening consequences of bariatric surgery require consequent interdisciplinary postsurgery care and therapy throughout the whole life, especially substitution therapy of deficiencies due to post-operative malassimilation, if necessary. Little is known about long term consequences of modified anatomy and function of digestive system caused by surgery, and there may be a delay of (many) years until manifestation of clinical problems.Obese diabetics (BMI ≥ 35 kg/m) should primarily be treated conservatively in an "individualized" way. Metabolic surgery should not be considered earlier than failure of the conservative approach has to be stated (in this case as an "ultima ratio" in well defined trials). A broader use of metabolic surgery beyond this narrow frame is not yet supported by long-term evidence-based data showing its value and safety.