Development and differentiation of bile ducts have been studied for the understanding of pathogenesis of biliary atresia and other diseases of the intrahepatic biliary tree. The aim of this study is to correlate the type of biliary structure with the size of the portal tract and the gestational age. Twenty-four human livers were studied. Fetuses were assigned to four gestational age groups: group I, up to 20 postfecundation weeks (PFW); group II, from 21–26 PFW; group III, from 27–32 PFW; and group IV, from 33–38 PFW. In each specimen, 30 portal tracts were classified as small, medium, or large according to the diameter of the portal vein. In order to identify the bile duct cells, the sections were immunolabeled with anti-cytokeratin antibody, and the biliary structure was classified as absent (bile ducts (BD) 5 0), presence of bile duct cells without lumen (BD 5 1), or presence of bile duct with lumen (BD 5 2). In the small portal tracts, either there were no biliary structures or just a few. There was a substantial increase in the number of medium portal tracts that included a bile duct as a function of gestational age. The majority of large portal tracts exhibited a bile duct. In human fetus up to 20 PFW, it is possible to find 70% of portal tracts without bile ducts, and at 38 PFW it is expected that more than 50% of the portal tract has a BD . 0. We suggest the use of the diameter of the portal vein and the gestational age for the quantification of biliary structures and the evaluation of maturity of intrahepatic biliary tree.