Autoimmune pancreatitis (AIP) is a benign, IgG4-related, fibroinflammatory form of chronic pancreatitis that can mimic pancreatic ductal adenocarcinoma both clinically and radiographically. Laboratory studies typically demonstrate elevated serum IgG4 levels and imaging studies reveal a diffusely or focally enlarged pancreas with associated diffuse or focal narrowing of the pancreatic duct. The pathologic features include periductal lymphoplasmacytic inflammation, obliterative phlebitis, and abundant IgG4-positive plasma cells. The treatment of choice for AIP is steroid therapy. Diagnostic criteria for AIP have been proposed that incorporate histologic, radiographic, serologic, and clinical information.