Autoimmune pancreatitis (AIP) is a rare disease that has recently emerged as a unique type of pancreatitis with a presumed autoimmune etiology. In 1995, Yoshida et al.  proposed AIP as a diagnostic entity. They summarized the clinical features of AIP as follows: increased serum γ-globulin or immunoglobulin (Ig)G levels and the presence of autoantibodies; diffuse irregular narrowing of the main pancreatic duct (MPD) and enlargement of the pancreas; occasional association with stenosis of the lower bile duct and other autoimmune diseases; mild symptoms, usually without acute attacks of pancreatitis; effectiveness of steroid therapy; and histological findings of lymphoplasmacytic sclerosing pancreatitis (LPSP) [1, 2]. Thereafter, AIP has been extensively reported worldwide including from Japan, Korea, Europe, and the United States. Because AIP is a relatively new clinical entity and the diagnostic criteria are being established, the epidemiology of AIP is not fully known. In Japan, the Research Committee of Intractable Pancreatic Disease provided by the Ministry of Health, Labour, and Welfare of Japan (RCIPD) has conducted three nationwide epidemiological surveys of AIP according to the diagnostic criteria used at that time. We here describe the epidemiology of AIP, mainly focusing on the results of nationwide surveys in Japan [3, 4].
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