Propylthiouracil (PTU) is a drug that's used to manage hyperthyroidism and it can, on rare occasions, induce antineutrophil cytoplasmic antibody-associated vasculitis that involves multiple organ systems and it can also cause extremely rare isolated or diffuse pulmonary hemorrhage. We report here on a case of a patient who developed diffuse pulmonary hemorrhage after she had been taking PTU for five years. The patient is a 33-year-old woman who presented with hemoptysis. Simple chest radiographs and the chest CT showed bilateral ground-glass opacity, consolidation and pulmonary arterial hypertension. The bronchoalveolar lavage fluid revealed alveolar hemorrhage. The laboratory values showed increased perinuclear-antineutrophil cytoplasmic antibody (p-ANCA) and anti-peroxidase antibody titers.