Annular pancreas (AP) is a rare cause of congenital duodenal obstruction that is usually discovered at the neonatal period, but clinical severities can vary over a wide range and definite diagnosis could be delayed until late childhood or adulthood. We report here a case of AP detected in an 11-year-old girl who had a long history of symptoms of partial duodenal obstruction. Upper gastrointestinal (UGI) study revealed narrowed second portion of duodenum by extrinsic compression, and computed tomography demonstrated complete ring of pancreatic tissue surrounding the second portion of the duodenum. Diamond-shaped duodenoduodenostomy successfully cured the patient, and the postoperative UGI study showed smooth passage through the bypass segment. Although rare, AP should be differentiated in children with unresolved symptoms of partial duodenal obstruction.