THE PRESENT dissertation is a report of 27 cases of congenital atresia of the extrahepatic biliary tract that have been encountered at The New York Hospital from 1932-1952. Although the condition occurs infrequently, more than 300 cases have been reported in the literature. Moore22 estimated that there is one case in 20,000 to 30,000 births. Jaundice in the newborn is not uncommon and may be a manifestation of physiologic icterus neonatorum, erythroblastosis fetalis, septicemia, syphilis, or obstruction of the biliary tract. Primary blood dyscrasias such as Mediterranean, congenital hemolytic, sickle cell, and acute hemolytic anemia are also associated with jaundice but tend to occur later in childhood. Physiologic icterus neonatorum is common, occurring to some degree in 50 to 75% of all newborn infants,21 and is manifested by a mild jaundice, appearing on the 2d or 3d day and disappearing usually by the 14th day. The liver is