Patients with hilar obstruction usually require bilateral biliary drainage. The prognosis of patients who fail bilateral biliary drainage after contrast injection into both intrahepatic ducts is poor due to a high infection rate in the undrained segments. The incidence of post–endoscopic retrograde cholangiopancreatography cholangitis in those with successful bilateral biliary drainage was less, but still significant. Incomplete subsegmental intrahepatic duct drainage is suggested to be responsible for post–biliary drainage cholangitis in cases of advanced hilar tumors. This study was undertaken to determine the incidence of post–endoscopic retrograde cholangiopancreatography cholangitis, jaundice resolution, and stent clogging in different types of malignant biliary obstruction after biliary drainage. From our endoscopic retrograde cholangiopancreatography database, there were 63 patients who underwent endoscopic biliary drainage between September 2000 and November 2001, for malignant biliary obstruction. Sixty-one endoscopic retrograde cholangiopancreatographies had biliary drainage performed (2 patients who failed biliary drainage were excluded). We divided our patients into 3 groups: Group 1 = Bismuth I, Group 2 = Bismuth II, and Group 3 = Bismuth III and IV. All but 2 Group 1 patients had successful biliary endoprosthesis (plastic [n = 13], metallic [n = 12], failed [n = 2]) placement into an extrahepatic duct. All patients from Group 2 (n = 10) and 20 patients from Group 3 (n = 26) had successful bilateral biliary drainage. Unilateral biliary drainage was performed in 6 patients from Group 3, each with a plastic endoprosthesis. The incidence of post–biliary drainage cholangitis (new onset of fever >38.5°C with leukocytosis), jaundice resolution (normal bilirubin level), and the duration of endoprosthesis patency were compared among the 3 groups. The incidences of post–endoscopic retrograde cholangiopancreatography cholangitis, jaundice resolution, and the duration of endoprosthesis patency were: Group 1 (4%, 96%, and 87.2 days, respectively), Group 2 (10%, 100%, and 69.1 days, respectively) and Group 3 (57.7%, 73.1%, and 41.3 days, respectively). Of those patients who did not undergo surgery, patients from Group 3 required endoprosthesis exchange sooner than others. The outcome of biliary drainage in patients with advanced hilar tumors (Bismuth III or IV) was poorer than hilar tumor at earlier stages (Bismuth I or II).