Angiosarcomas are malignant vascular tumors. Angiosarcomas arising in the thorax such as angiosarcoma of the lungs, heart and mediastinum are extremely rare. There are no reports of mediastinal angiosarcomas presenting with diffuse alveolar hemorrhage, which is a clinical syndrome characterized by the presence of hemoptysis, dyspnea, hypoxia, diffuse lung infiltrates and anemia. Usually, diffuse alveolar hemorrhage is caused by pulmonary capillaritis. Local invasion is more common with these tumors than distant metastasis. These tumors are very aggressive and have a poor response to treatment modalities including surgical resection, chemotherapy, and radiation. Consequently, they carry a poor prognosis. Due to the rarity of these tumors, no standard chemotherapy or radiation protocol exists. We report a case of diffuse alveolar hemorrhage caused by a previously unreported entity: angiosarcoma of the mediastinum.