The liver and the biliary tract are rich in anatomical variations, knowledge of which is important for the surgeon. A case of an anatomical variation is reported, which allowed easy and oncologically correct resection of a Klatskin tumour. The variation consisted of abnormally long right and left extrahepatic ducts and an abnormal distal bifurcation, with a cystic duct joining the distal end of the right duct. A favourable modification of surgical strategy could be obtained by an oncologically correct resection of a Klatskin tumour avoiding a liver resection and also allowing easy reconstruction. Complete biliary exposure was necessary to reveal the rare, pre-operatively unrecognized, but favourable situation. In the absence of clear contraindications extended biliary dissection is to be recommended to avoid errors in the evaluation of the resectability of hilar biliary cancers.