Methimazole, carbimazole, and propylthiouracil (PTU) are the mainstays of antithyroid drug therapy. Adverse effects of these drugs have been documented in less than 15% of patients undergoing treatment for hyperthyroidism. Common problems include fever, skin rash, urticaria, arthralgias, and arthritis. Vasculitis associated with antineutrophil anticytoplasmic antibodies (ANCA) has been reported on several occasions following treatment with PTU. However, vasculitis rarely appears to be associated with carbimazole. We report the clinical history of a woman with a necrotizing glomerulonephritis and pulmonary hemorrhage associated with carbimazole therapy.