A 67-year-old man had undergone a right ureteronephrectomy because of a right ureter tumor, but the pathological diagnosis was inflammatory tissue with plasma cells, lymphocytes, and fibrosis. About 3 years later, abdominal computed tomography (CT) revealed a solid tumor at the left renal hilus. We resected the tumor and the pathological diagnosis was the same as before. More than 2 years later, because of elevated pancreatic enzymes, immunoglobulin G (IgG) and IgG4, more detailed examinations ware done, and he was diagnosed with IgG4-related autoimmune pancreatitis. We believe that the retroperitoneal tumor was retroperitoneal fibrosis associated with IgG4-related sclerosing disease. Now, he is being treated with steroid therapy. IgG4-related sclerosing disease is a systemic disease whose concept is now being established. Much more work is needed to understand this disease.