Functional and metabolic syndromes after surgery of the upper gastrointestinal tract (including the pancreas) are frequent. Resections of organs mandate the reconstruction with a change of anatomy. Predominantly, the reconstruction using a Y-en-Roux jejunal loop is used. The surgical alteration of the anatomy may lead to a different physiology. Patients after esophagectomy or gastrectomy may suffer from dysphagia, dumping syndromes, reflux and anaemia. Pancreatic resections or drainage operations may cause an exocrine or endocrine insufficiency. Patients after surgery for gastroesophageal reflux or achalasia may have gas-related symptoms such as bloating and flatulence. The treatment options of these syndromes include physical measures, drugs, interventional procedures and even revisional surgery. Detailed preoperative information of the procedure and multidisciplinary postoperative treatment (general practitioner, surgeon, gastroenterologist etc.) of evolving functional syndromes is mandatory to achieve a high standard of care.