BACKGROUND The majority of patients who require palliation for jaundice and pruritus resulting from malignant hilar obstruction are treated by stenting. Stenting is usually achieved from below after performing an endoscopic retrograde cholangiopancreatography. In some cases the rendezvous technique is employed, negotiating the passage through a malignant stricture from above and stenting from below. A minority of cases, such as those who had a previous polyagastrectomy and those in whom attempts at stenting have failed, are considered to be suitable for a Segment III cholangiojejunostomy. We have investigated the anatomical basis for Segment III duct bypass and have critically analysed the results in 13 patients. Ten patients were treated by Segment III duct bypass alone, and three patients had a Segment III duct bypass combined with stenting of the right liver. METHODS The anatomy of the biliary tree was investigated by dissection of 54 normal livers removed at autopsy. Clinical details of the 13 patients who had Section III cholangiojejunostomy were obtained from hospital records and by contacting treating practitioners. RESULTS In 64.8% of the anatomical dissections, the findings were favourable for a Section III cholangiojejunostomy. In these specimens the Segment III duct bypass would have drained Segments II, III and IV. In 35.2% of the specimens the anatomical disposition was potentially unfavourable, mainly due to the Segment II or IV ducts joining close to the confluence and therefore liable to obstruction by the tumour. In nine of the 54 specimens the true left hepatic duct was less than 6 mm in length, making it unsuitable for a bypass procedure to drain the left hemi liver. Of the 10 patients who were subjected to a palliative Section III cholangiojejunostomy only, there was one postoperative death. Of the nine patients who survived, six obtained excellent palliation of jaundice and pruritus. CONCLUSIONS In carefully selected cases, Section III cholangiojejunostomy achieves excellent palliation in patients with unresectable hilar malignancies that have been unable to be stented pre-operatively or who have unresectable tumours at the time of laparotomy.