Alimentary tract duplication is a rare congenital malformation but can occur anywhere along the digestive tract. Most patients become symptomatic in early childhood, and only a few cases of adult patients have been reported in the literature. We herein report a unique case of a giant ileal duplication in an adult, which was successfully treated with laparoscope-assisted surgery. A 60-year-old male was admitted because of abdominal pain. Imaging studies revealed a well-defined cystic mass, measuring 15 cm, in the ileocecal region. We diagnosed it as a duplicated ileum and performed laparoscope-assisted surgery. The duplication was successfully resected with attached normal ileum, and there were no major complications in the postoperative course.