Background: An ectopic opening of the common bile duct in the duodenal bulb is extremely rare, and the clinical significance of this anomaly has not been clarified. This study analyzed the clinical implications and cholangiographic findings of this anomaly. Methods: A total of 18 patients (15 men, 3 women; median age, 51 years) with an ectopic opening of the common bile duct in the duodenal bulb were studied. Medical records, endoscopic findings, and cholangiographic and other radiographic findings were reviewed. Results: All 18 patients had biliary pain; 7 had fever and chills. Fifteen (83%) had diffuse dilatation of the extrahepatic bile ducts with or without intrahepatic bile duct dilation. Associated bile duct stones were found in 10 (56%) patients. The papilla in the bulb had an orifice stained with bile at endoscopy, which was associated with duodenal ulcer disease found in 13 (72%) patients. The distal end of the common bile duct was tapered and narrowed and had a hook shape in all patients. Conclusion: An ectopic opening of the common bile duct in the duodenal bulb may be associated with clinical entities such as recurrent or intractable duodenal ulcer, choledocholithiasis, or acute cholangitis. Although these openings are rare, knowledge of the endoscopic and radiographic findings of an ectopic opening of the common bile duct in the duodenal bulb may help to clarify the cause of chronic recurrent duodenal ulcer disease in some patients and prevent damage to the bile duct during surgery. (Gastrointest Endosc 2003;57:679-82.)