Obstructive jaundice due to hilar cholangiocarcinoma is difficult to decompress because of the location of the tumor. We used external radiation alone for biliary decompression and reviewed its efficacy in this study. Subjects comprised 14 patients diagnosed as having inoperable hilar cholangiocarcinoma by ultrasonography, percutaneous transhepatic cholangiography, and CT scanning. The total bilirubin level on admission ranged from 0.4 to 34.6 mg/dl (mean: 11.0 mg/dl). These patients were irradiated with a 4MeV linear accelerator using parallel opposing fields measuring from 7 x 7 cm to 8 x 10 cm. The total radiation dose ranged from 50 Gy to 60 Gy and in fractions of 1.8-2.0 Gy per day. No patient underwent further biliary decompression after percutaneous transhepatic cholangiography, and irradiation was performed immediately after diagnosis. Eleven of the 14 patients received the full dose of external radiation. Three patients discontinued radiotherapy because of severe vomiting and nausea, pneumonia, and a hemorrhagic gastric ulcer. In 10 of the 11 patients, the serum total bilirubin level returned to normal (p < 0.005) and no cholangitis occurred. Obstructive jaundice recurred in one patient, and serum total bilirubin returned to normal again after further irradiation. Eight of the 11 patients could be discharged from hospital and returned to society. The survival time of the 11 patients ranged from 3 to 25 months and the 12-month survival rate was 50% (Kaplan-Meier method). This study suggests that external radiation therapy is an effective treatment for biliary decompression in patients with unresectable hilar cholangiocarcinoma.