Congenital duodenal web in adult life is an extremely rare condition, which results from an incomplete recanalization of the duodenum during early embryologic development. We report a case of congenital duodenal web in a 23-year-old man who complained of postprandial epigastric pain and fullness, as well as nausea since childhood. The plain abdomen showed a double-bubble sign. The UGI study showed a marked dilatation of the proximal duodenum and a delayed passage of barium into the third portion of the duodenum. Abdominal ultrasonography and CT revealed a marked dilatation of the proximal duodenum and a duodenal web with windsock deformity, which originated from the ampulla of Vater and extended to the third portion of the duodenum. A winsock web with a 0.9 cm eccentric aperture and a healed ulcer proximal to the ampulla of Vater were observed during a longitudinal duodenotomy. The web was excised circumferentially and the duodenum was closed transversely in a Heineke-Mikulicz fashion.