Conjugated hyperbilirubinemia in the newborn period and early infancy can result from choledochal obstruction or hepatocellular damage. Examples of the former include biliary atresia, choledochal cyst, and choledochal bile plugs. The recognition of these conditions and their differentiation are of importance in determining the best and most effective course of therapy. Choledochal cysts and bile plugs can be corrected surgically, and the presence of these two conditions is best determined by surgical exploration and transcholecystic cholangiography. Previous liver biopsy is helpful in establishing the presence of an obstructive lesion; but, because of the similarity of histopathological effects on the liver, it will be of little help in differentiating the causes of obstruction.