We describe a case of IgG4-related lung disease presenting as a lung mass with associated weight loss. IgG4-related disease is a systemic sclerosing disorder that causes fibrotic, often tumor-like manifestations that variably effect different organ systems. The clinical presentation of IgG4-related disease is protean. Timely recognition and diagnosis requires awareness on the part of clinicians and pathologists to the variable manifestations of this newly recognized disorder. We offer a concise review of the pulmonary manifestations, diagnosis and treatment of IgG4-related lung disease.