Familial occurrence of extrahepatic biliary atresia (EHBA) or biliary dilatation has been reported; however, the genetic influences on these disorders are still obscure. The authors previously reported the occurrence of biliary dilatation and EHBA in sisters, which is extremely rare. Recently, a similar pair of sisters was treated; one had pancreaticobiliary maljunction with minimal dilatation of the common bile duct, and the other also had EHBA. The authors' investigations suggest that there may be common etiologic factors for EHBA and biliary dilatation, such as pancreaticobiliary maljunction; however, other factors are required to complete the process and cause biliary atresia.