Immunoglobulin G subclass 4 Related Disease (IgG4-RD) is a recently recognized systemic fibroinflammatory condition. Various manifestations of IgG4-RD were previously recognized in individual organ systems, but these entities (including autoimmune pancreatitis, orbital pseudotumor, Reidel's thyroiditis, retroperitoneal fibrosis, idiopathic sialadenitis and dacryoadenitis, etc) are now recognized as manifestations of a common disease process that can affect any organ system. IgG4-RD is characterized by distinctive histologic findings of tissue infiltration by IgG4-positive plasma cells together with storiform fibrosis and obliterative phlebitis. Both clinical and pathologic consensus diagnostic criteria have been defined. Serum IgG4 concentration is a biomarker for IgG4-RD and is elevated in 70% to 90% of patients with active disease.