We describe a 47-year-old woman with severe coronary vasospasm induced by hyperthyroidism. The patient complained of anginal chest pain without specific characteristics of thyrotoxicosis. Coronary arteriography was performed and revealed 90% stenosis of both the left and right coronary os. She was treated with emergent coronary artery bypass graft surgery. Postoperatively, she exhibited a comatose mentality. Severe thyrotoxicosis was indicated on thyroid function tests and thyrotoxic storm was diagnosed. Nineteen days after the surgery and following the initiation of propylthiouracil treatment, coronary arteriography revealed entirely normal coronary arteries.