In recent years autoimmune pancreatitis (AIP) has been established as a special type of chronic pancreatitis. It is characterized by its histopathological and immunological features. The morphological hallmarks are periductal infiltration by lymphocytes and plasma cells, granulocytic epithelial lesions with focal destruction of the duct epithelium, venulitis, and diffuse sclerosis in advanced stages. AIP has therefore also been called lymphoplasmacytic sclerosing pancreatitis, duct-destructive chronic pancreatitis, or sclerosing pancreatitis. AIP most commonly involves the head of the pancreas and the distal bile duct. Occasionally it is mass-forming, and has been described as an inflammatory myofibroblastic tumor. The presence of more than 20 IgG4-positive plasma cells per high-power field is of high specificity for the tissue diagnosis of AIP.