Reports about FDG PET in biliary tumor are limited and there are almost no reports regarding its efficacy. Biliary tumor is divided to intahepatic and extrahepatic bile duct cancer, and intrahepatic bile duct cancer can be further divided to peripheral type which occurs at lobular duct and hilar type which occurs at hepatic hilum. Surgical resection is the only curative method for bile duct tumor, and accurate staging plays an important role in deciding treatment modality. Among intrahepatic bile duct tumors, peripheral type and hilar type have the same histological characteristics, but different clinical manifestations and tumor growth pattern. On PET image, FDG uptake is also different between peripheral type and hilar type. Most of the former shows high FDG uptake at primary and metastasis site so it is very useful for determining stage and changing treatment plans. However, the later is diversified among low uptake and very high uptake. The FDG uptake pattern of hilar type is similar to that of extrahepatic bile duct cancer, and mucinous component is an important factor, which affects FDG uptake. When tumor cells are scattered in desmoplatsic stroma, then FDG uptake is low as well. In contrast, when FDG uptake is high, it is likely to be tubular type which has high tumor density. Tumor growth pattern also affects FDG uptake. Nodular type mostly takes higher FDG compared to infiltrative type. There are many cases where benign inflammatory diseases take high FDG that PET alone can not distinguish malignant lesion from benign lesion. In conclusion, studies about PET using FDG are still limited. Thus, it is hard to make accurate conclusion about the roles of PET or PET/CT in biliary cancers, but peripheral type intrahepatic bile duct cancers and mass forming hilar and extrahepatic bile duct cancers appear to be good indications performing FDG PET or PET/CT. (Nucl Med Mol Imaging 2008;42(suppl 1):66-70)