Biliary tract cancer is a rare cancer in most parts of the world, but it is relatively common in some countries and ethnic groups, such as Japan, Central and South America, eastern Europe and in American Indians, and Hispanics. In some countries, such as Japan, Sweden, Finland and Italy, the age adjusted mortality of biliary tract cancer has been increasing, whereas in females in some other countries--Israel, The Netherlands, USA, Canada, Federal Republic of Germany, etc--mortality has been declining. The reasons for these geographical or ethnic variations and time trends for biliary tract cancer are not clear, but some unknown environmental risk factors or a genetic susceptibility are suspected. Not many analytical epidemiological studies on biliary tract cancer have been conducted yet and little is known about its aetiology apart from a close association with gall stones and a female preponderance of gall bladder cancer. Besides gall stones, some other factors such as obesity, pregnancy, female sex hormones, exposure in rubber and some other chemical industries and genetic factors have been suspected of being associated with gall bladder cancer directly or indirectly through cholelithiasis. As an artificial factor, the effect of the prevalence of cholecystectomy on biliary tract cancer must be considered. More studies are needed in the future to elucidate the aetiology of biliary tract cancer and to establish measures to prevent this cancer.