A 50-year-old woman had been treated with propylthiouracil (PTU) for hyperthyroidism. She was admitted to our hospital because of hemosputum, and severe hypoxemia developed. The CT scan showed diffuse infiltration in both lung fields, bronchoalveolar lavage fluid revealed diffuse alveolar hemorrhage, and the level of myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA) was high; and therefore diffuse alveolar hemorrhage associated with MPO-ANCA positive vasculitis induced by PTU was diagnosed. Following corticosteroid therapy initiated after the termination of PTU, the pulmonary infiltration rapidly improved and the patient's MPO-ANCA level returned to normal. Recrudescence of diffuse alveolar hemorrhage occurred following a reduction in steroids, but no recurrence was found after cyclophosphamide therapy was combined with steroid therapy. During the course of therapy, various cardiac conducting system abnormalities which correlate with the course of steroid therapy were found, indicating that cardiac conducting system abnormalities may be associated with MPO-ANCA-positive vasculitis.