Extrahepatic biliary atresia is a liver disease presenting in early infancy, manifested by progressive obliteration of the extrahepatic bile ducts. It has been estimated to occur in from one per 8000 to one per 15000 live births, and is the single most common indication for performance of liver transplantation in children. None of the incidence figures is based on a well defined geopolitical region; most estimates of the frequency of this condition are derived from referral centers. Some investigators have suggested a time-space clustering of this condition. This project will gather information on all cases in a well defined geopolitical area for approximately 10 years, and birth certificates will be obtained. Cases will be compared to the other births in the area for evidence of changes in incidence and clustering. It is anticipated that a site will be selected and field work begin in 1986.