Gallstones are common in Western countries and Japan. Most gallstones are found in the gallbladder, but they sometimes pass through the cystic duct into extrahepatic and/or intrahepatic bile ducts to become bile-duct stones, causing conditions known as choledocholithiasis and hepatolithiasis. Some 10-15% of gallstone patients concomitantly suffer from bile-duct stones. Bile-duct stones can also be formed in the absence of gallbladder stones, and such primary bile-duct stones are more common in East Asian countries than in the Western world. Thus pathogenesis of primary and secondary bile-duct stones is unlikely to be similar. Furthermore, the gallbladder stones are primarily cholesterol or black-pigment stones, whereas most bile-duct stones are brown-pigment stones (calcium bilirubin stones). Thus, epidemiology, pathogenesis and classification of biliary stones are very likely to differ according to stone location (intrahepatic and/or extrahepatic bile duct).