A 21-year-old man with a developmental disability presented for management of upper abdominal pain and vomiting. He was diagnosed by endoscopy and computed tomography-duodenography as having duodenal obstruction due to duodenal duplication. He underwent endoscopic resection of the blind end of the duplication and was discharged on the ninth postoperative day. In a follow-up endoscopy 6 weeks after treatment, the scope passed smoothly and it was found that an iatrogenic ulcer postendoscopic resection had healed. Duodenal duplication is rare, and few cases have been diagnosed preoperatively in detail with imaging and undergone successful endoscopic treatment, as in the present case.