A case of choledochocele, which is an Alonso-Lej type III congenital biliary dilatation, associating with stones only in the cyst is experienced.A 39-year-old woman was admitted to the hospital because of submucosal tumor of the duodenum which was pointed out by endoscopic examination at medical checkout. Sometimes the patient had mild right hypochondralgia but she did not consult with any hospital. On this admission abdominal ultrasonography, CT, and ERCP revealed choledochocele of Scholz type B associating with stones in the cyst. Operation was carried out. On laparotomy levels in pancreatic enzymes such as amylase in the cystic bile juice were high; an opening 1 mm in size was found in the posterior wall of common duct due to papilloplasty and 3 stones were found in the cyst. The cyst wall was excised and sutured with the duodenal wall. Histologically the internal surface of the cyst was consisted of duodenal mucosa, and no malignancy was noted in the gallbladder. This case is the 59th in Japan. The disease is associated with stones and pancreatitis, as well as a malignant neoplasm in a relatively high rate. Probable actions of pancreatic enzymes to the cyst wall and biliary tract are inferred, where intra and postoperative histological exploration would be also necessary.