Annular pancreas as a cause of extrahepatic biliary obstruction. Annular pancreas is a rare congenital abnormality that is increasingly diagnosed by endoscopic retrograde cholangiopancreatography (ERCP) in the adult. In this population, it can present with duodenal or gastric ulceration, duodenal obstruction, pancreatitis, and, rarely, with associated congenital abnormalities. Although it has been suggested that biliary obstruction may result from associated pancreatitis, such cases have not been reported; primary extrahepatic biliary obstruction from a constricting annulus also has not been reported. We report such a case, and describe resolution of symptoms and a return to normal biochemical tests in a patient. The literature and embryology of annular pancreas are reviewed. We suggest that this entity be added to the differential diagnosis of extrahepatic biliary obstruction. 