We report a very rare case of autoimmune pancreatitis (AIP) associated with sclerosing cholangitis, retroperitoneal fibrosis and Sjögren's syndrome. The patient had an enlarged pancreas, and autoantibodies were detected in the serum. Serum IgG and IgG4 concentrations were also elevated. Endoscopic retrograde cholangiopancreatography revealed an irregular narrowing of the main pancreatic duct from the head to the body and sclerotic change in the intrapancreatic common bile duct, which later extended to the intrahepatic bile ducts. In addition, histological examination of the liver revealed lymphocytic sclerosis around the bile ducts, similar to the histology in the pancreas of AIP. Retroperitoneal tumors were diagnosed as retroperitoneal fibrosis by histological examination. Serological and functional abnormalities suggestive of Sjögren's syndrome were detected, and histological findings of the lip were compatible with Sjögren's syndrome. Immunohistochemistry of each lesion disclosed that most of the infiltrating lymphocytes were T cells with similar levels of both CD4+ and CD8+ cells. Moreover, some of the infiltrating plasma cells were positive for anti-IgG4 monoclonal antibody. These diseases were dramatically improved by steroid therapy. Although the pathophysiology of AIP is still unclear, the present case suggests a common pathophysiological mechanism for AIP, sclerosing cholangitis, retroperitoneal fibrosis and Sjögren's syndrome.