It is uncommon that Anesthesiologist experience thyroid storm during the elective surgery because of marked reduction of operation for the treatment of hyperthyroidism owing to the development of radio-active iodide, antithyroid drugs and the use of beta-receptor blockers such as propranolol. In the treatment of Graves' disease, the conditions such as persistant symptoms of hyperthyroidism with resistance to the antithyroid drugs, frequent relapses and increasing size of thyroid gland must be considered for the need of surgery. It is essential to maintain the euthyroid state before surgery in these cases, if not, the possibility of thyroid storm is increased from increased release of thyroid hormones owing to manipulation of surgery. In our case, the patient had been medicated for 6 years, however, the euthyroid state had not been achieved before the day of surgery. Under the judgement of difficulty for more control of hyperthyroidism the surgeon requested for operation without delay. Immediately after starting operation, the symptoms suggesting thyroid storm such as the abrupt onset of high fever, the increasing blood pressure and heart rate were occured. The sugery was stopped and then the management for thyroid storm was begun. At arterial blood gas analysis, respiratory acidosis and metabolic acidosis were developed and increased hilar haziness suggesting severe pulmonary edema were present in both lung fields at chest x-ray. The patient was mechanically ventillated until improvement of metabolic and respiratory acidosis and pulmonary edema. Two days after operation, vital signs were stabilized and the patient was transferred to general wards.