Duodenal duplication, a rare congenital malformation,can also be observed in adulthood. Although it can be cystic or tubular, communicating or noncommunicating, cystic and non-communicating forms are the most common. Several complications, such as obstruction, bleeding, perforation and pancreatitis, may result. Optimal treatment is total excision,although endoscopic procedures have also been described in appropriate cases. If total excision is not possible, subtotal excision and intal derivation can be performed. The 38-year-old woman presented here had occasional attacks of abdominal pain and obstruction, and we considered the diagnosis of duodenal duplication by abdominal computerized tomography. As we confirmed the diagnosis with operative findings and histopathological signs, we treated her with subtotal excision and intraduodenal cystoduodenostomy.