Obesity is a growing health problem in most parts of the world. Currently only proven long term effective treatment of obesity is bariatric surgery. Roux & Y gastric bypass together with sleeve gastrectomy are the most employed surgical techniques with acceptable metabolic and surgical complication rates. In this paper we would like to present an unexpected complication of Roux & Y gastric bypass: a retrograde intussusception located in the common limb 17 months after the surgery. As intussusception in adults usually originates from a leading point, there is no such an explanation following Roux & Y gastric bypass.