Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disease with protean manifestations involving virtually any organ in the body. At initial clinical presentation, 1 or multiple organs may be involved. Initial descriptions focused on pancreatic disease. It has, however, become clear that IgG4-RD can cause an immune-mediated fibroinflammatory process, commonly manifesting as mass-like lesions, in various regions of the body including the thorax where any compartment can be involved. This pathologic process is characterized by infiltration of IgG4+ plasma cells and a propensity to fibrosis leading to organ dysfunction which can be prevented by early diagnosis and corticosteroid therapy.