In Belgium and around the world, the weight-control surgery has grown significantly since the beginning of the 21st century. The principal argument in favour of this type of surgery is the expected reduction of the obesity-associated morbidities. However, the expectatif reduction of mortality associated with this kind of surgery is based on a low level of evidence. Besides the mechanical complications, there are a number of health-related problems associated with the post-operative metabolic changes. Authors of the present article have observed four cases presenting with serious affections consecutive to bariatric interventions and reviewed the literature. The most frequent consequence of bariatric surgery is anaemia (15%), which is either due to iron or cyanocobalamine deficiency, followed by neuropathies, bone mineral loss, substance abuse or postprandial hypoglycaemia syndrome. Rare but severe complications are Wernicke's encephalopathy, fulminant hepatitis or hyperoxaluric tubular disease. The prevention, diagnosis and management of these new diseases are becoming a major public health concern.