The findings in 107 cases of perivaterian diverticulum diagnosed by endoscopic retrograde cholangiopancreatography (ERCP) were discussed in relation to complicated biliary tract disease. The incidence of abnormality in both gallbladder and bile duct, especially in extrahepatic bile ducts, was more frequent in cases of perivaterian diverticuli more than 11 mm in diameter. Perivaterian diverticuli was most frequently located on the oral side of papilla. Cases with papilla in a diverticulum showed more frequent biliary tract abnormality. Abnormal findings of the distal portion of common bile duct, such as flexion, compression and tapering, were noted in 31% of 107 cases. These findings were seen more frequently in cases with papilla in a diverticulum or with a diverticulum more than 11 mm in diameter. It is considered that these data suggest a mechanism of occurrence of biliary tract disease in cases with perivaterian diverticulum.