The case of a 31-year-old male is reported who had recurrent, unexplained abdominal complaints. After hospitalization, an ileus was localized by plain abdominal film in the ileocecal region. A contrast meal revealed a typical intraluminal (duodenal) diverticulum with an enlarged prestenotic duodenum that was undetected during endoscopy. At operation, the cause of the ileus was revealed to be a phytobezoar near the ileocolic valve. After removal and after transluminal resection of the diverticulum, the postoperative course was uneventful. The authors discuss the importance of early roentgen cinematography to clear up the pathogenesis of this very rare intraluminal lesion.