Purpose To seek for the possible factors influencing overall survival (OS) with radiotherapy (RT) for biliary tract cancer. Materials and methods Data were collected retrospectively from RT database of 31 institutions in Japan. All patients underwent at least external beam RT. The factors influencing OS were investigated. Results Data of 498 patients were analyzed. Median OS of the 212 patients who underwent surgery was significantly better than that of the 286 patients without surgery (31 vs. 15 months, p < 0.001). The OS for the R0 or R1 resection group was significantly longer than that for the R2 or non-surgery group, as well as for n0 compared to n1 (all p < 0.001). Chemoradiotherapy (CRT), both sequential and concurrent, resulted in a better OS than RT alone for the n1 group (31 vs. 13 months, p < 0.001), and marginally better for the R0/R1 group (p = 0.065; p = 0.054 for concurrent CRT). However, no such benefit was observed for the R2/non-surgical patients. Multivariate analysis identified performance status, clinical stage, and surgery as significant factors. Conclusion Surgery, especially R0/R1 resection, seemed as the gold standard for treatment of biliary tract cancer including RT, even in the highly heterogeneous population obtained from the multicenter retrospective study. The possibility was shown that CRT yielded better survival benefit especially for n1 patients. We recommend that future prospective trials include an arm of adjuvant CRT at least for n1 and possibly R0/R1 patients. © 2013 Elsevier Ireland Ltd. All rights reserved.