A 35-year old man with cough, hemoptysis, and dyspnea was found to have diffuse pulmonary infiltrates and iron-laden macrophages in the sputum. Pulmonary siderosis was confirmed by transbronchial biopsy. An associated hypochromic anemia required frequent transfusion. Though marrow iron stores were absent, reticulocytosis was maintained. Corticosteroid therapy resulted in cessation of hemoptysis, clearing of the pulmonary infiltration, and a substantial reduction in transfusion requirement. Splenectomy was of no benefit. The patient developed cerebral symptoms with seizures, and rapid deterioration led to cerebral symptoms with seizures, and rapid deterioration led to death. Disseminated hemangiosarcoma was found at autopsy. Steroid responsiveness of the associated pulmonary siderosis suggests that it had an immune basis.