Immunoglobulin (Ig)G4-mediated disease is a systemic autoimmune disease, which occasionally presents solely as sclerosing cholangitis (SC). IgG4-mediated SC is challenging to diagnose, as it may mimic cholangiocarcinoma radiologically, and carcinoma cells may produce IgG4. The diagnosis of IgG4-mediated disease is based on histological consensus criteria and response to corticosteroids. In addition to the radiological and histological overlap between IgG4-mediated SC and cholangiocarcinoma, IgG4-mediated SC may be considered as a risk factor for the development of cholangiocarcinoma. We herein present the case of a patient in whom cholangiocarcinoma developed in two lesions previously characterized as IgG4-mediated SC, including a suggested mechanism underlying the contribution of IgG4-mediated SC to the development of cholangiocarcinoma.