When diagnosing autoimmune pancreatitis (AIP), it is most important to differentiate it from neoplastic lesions such as pancreatic or biliary cancers. The revised diagnostic criteria are based on the minimum consensus of AIP in order to avoid misdiagnosing pancreas or biliary cancer as far as possible, but not for screening AIP. Therefore, it is recommended that facile therapeutic diagnosis by steroidal administration should be avoided. These criteria contain three approaches: pancreatic imaging, laboratory data, and histopathology. (i) Pancreatic image examinations show the narrowing of the main pancreatic duct and enlargement of the pancreas, which are characteristic of the disease. (ii) Laboratory data show the presence of autoantibodies or elevated levels of serum gammaglobulin, IgG, or IgG4. (iii) Histopathologial examinations of the pancreas show fibrosis and pronounced infiltration of cells, mainly lymphocytes and plasmacytes, which is called lymphoplasmacytic sclerosing cholangitis (LPSP). For a diagnosis of AIP, criterion (i) must be present, together with criterion (ii) and/or (iii). However, it is necessary to exclude malignant diseases such as pancreatic or biliary cancers.