Primary giant-cell tumors rarely arise in the common bile duct.We herein report a case of primary giantcell tumor of the common bile duct.The patient was an 81-year-old male who was diagnosed with a welldefined 1.2-cm mass projecting into the lumen of the middle common bile duct.Excision of the gallbladder and extrahepatic bile duct and a Roux-en-Y cholangiojejunostomy were performed.Histologically,the tumor had no association with carcinomas of epithelial origin and was similar to giant-cell tumors of the bone.The tumor consisted of a mixture of mononuclear and multinucleated osteoclast-like giant cells.The mononuclear cells showed no atypical features,and their nuclei were similar to those of the multinucleated giant cells.CD68 was expressed on the mononuclear and multinucleated osteoclast-like giant cells,whereas CD163 immunoreactivity was restricted to the mononuclear cells.Six months after the operation,the patient was still alive and had no recurrence.The interest of this case lies in the rarity of this entity,the difficulty of preoperative diagnosis,and this tumor’s possible confusion with other malignant tumors. Primary giant-cell tumors rarely arise in the common bile duct. We reported report a case of primary giant cell tumor of the common bile duct. The patient was an 81-year-old male who was diagnosed with a well defined as 1.2-cm mass projecting into the lumen of the middle common bile duct. Exision of the gallbladder and extrahepatic bile duct and a Roux-en-y cholangiojejunostomy were performed. Histologically, the tumor had no association with carcinomas of epithelial origin and was similar to giant-cell tumors of the bone.The tumor consisted of a mixture of mononuclear and multinucleated osteoclast-like giant cells. mononuclear cells showed no atypical features, and their nuclei were similar to those of the multinucleated giant cells. CD68 was expressed on the mononuclear and multinucleated osteoclast-like giant cells, while CD163 immunoreactivity was restricted to the mononuclear cells. Six months after the operation, the patient was still alive and had no recurrence. the interest of this case li es in the rarity of this entity, the difficulty of preoperative diagnosis, and this tumor’s possible confusion with other malignant tumors.