Abstract
A 7-month-old boy was transferred to our hospital under the diagnosis of irreducible intussusception. A laparotomy revealed an ileal duplication cyst closely associated with a diverticulum of the terminal ileum. Neither lesion was located at the mesenteric side attatchment to the ileum. We performed diverticulectomy and wedge resection of the duplication cyst to preserve the ileal valve. There have been some theories about the embryogenesis of alimentary tract duplication, however, close association of duplication and diverticulum, like that presented our case, might be explained by Lewis & Thyng's "embryonic diverticula" theory.