As opposed to congenital anomalies, the anatomical variations, as well as the modal type, are issued from a normal morphological development. The variations of division of extra-hepatic biliary ducts are very frequent. They are clearly explained by the sequence of embryological development in man, and also by compared anatomy. Lots of variations occur, some of them being more frequently encountered than others during cholecystectomy for gallbladder lithiasis. A cysto-hepatic duct draining a large hepatic territory is the most dangerous variation. As a matter of fact, it can look as if the junction between the cystic duct and the common biliary duct was of the modal type. In surgical practice, the dissection of cystic duct must never go over the right side of the common biliary duct in order for it never to be injured. Radiological exploration of biliary tree during cholecystectomy for gallbladder lithiasis has to be routine, in order to discover the obviously unpredictable individual variations of division of extra-hepatic biliary ducts.