A primary carcinoma of the cystic duct is extremely rare, accounting for 2.6% of all biliary carcinomas. However, the prognosis is better than other biliary carcinomas. The median survival is 20.4 months. In Korea, three cases have been reported and there is no case where a pre-operative MRI has been performed. We report a case of a primary carcinoma of the cystic duct with hepatic duct invasion, which presented as a painless right upper quadrant mass, that was diagnosed by MRCP in a pre-operative situation. (Korean J Gastrointest Endosc 2006;33:178182)