BACKGROUND/AIMS: The technique of cholangioscopy has been used in the treatment of bile duct stones or for the diagnosis of various bile duct tumors. However, the cholangioscopic characteristics of the various types of bile duct tumors have not yet been clearly described. Therefore, we analyzed the results of our cholangioscopic examinations and classified the cholangioscopic findings according to tumor histology. METHODS: The cholangioscopic finding from 111 patients who had benign or malignant bile duct tumors were reviewed. The mucosal changes, the presence of neovascularization, and the patterns of luminal narrowing were analyzed and compared with the histologic diagnosis. RESULTS: Bile duct adenocarcinoma can be classified into three different types according to the cholangioscopic findings: nodular, papillary, and infiltrative. Bile duct adenoma, hepatocellular carcinoma and other types of bile duct cancer such as mucin-hypersecreting cholangiocarcinoma, biliary cystadenocarcinoma, squamous cell carcinoma also presented with their unique cholangioscopic characteristics. CONCLUSIONS: Bile duct tumors seem to show characteristic cholangioscopic findings according to their histology. Cholangioscopic examination seems to be a useful technique in the differential diagnosis of bile duct tumors.