A patient with obstructive jaundice due to carcinoma of the pancreas head showed painless vomiting from the supra-papillary duodenal obstruction. Computed tomography demonstrated a space-occupying lesion in the head of the pancreas, which was not so large as to make an obstruction of the proximal portion of the duodenum. Pylorus preserving pancreatoduodenectomy was performed and the surgical specimen showed that the duodenal obstruction was caused by a swollen annular pancreas associated with obstructive pancreatitis by the carcinoma of the pancreas head. Duodenal obstruction is a rare symptom of annular pancreas in adults. It is thought to be necessary to remind of the coexistence of the annular pancreas, when patients with pancreatic or periampullary malignancies are complicated with unexpected obstruction of the second portion of the duodenum in proportion to the size.