A 39-year-old female without any specific past history was scheduled to receive an operation for myoma uteri and ovarian cyst. She was premedicated with atropine. Anesthesia was induced with thiopental and was maintained with nitrous oxide and enflurane. Tachycardia shortly after premedication with atropine and remarkable sweat during the operation were observed. On the 1st postoperative day an outbreak of thyroid crisis as well tachycardia of 180.min-1 and fever (39.3 degrees C) were observed. Such outbreak of thyroid crisis indicated that the patient had been suffering from Grave disease. Pathological diagnosis of extirpated ovarian cyst was struma ovarii. It is, however, still uncertain whether struma ovarii induced thyroid crisis in this case. It might be concluded that screening of hyperthyroidism at preoperative rounds is essential for prevention of thyroid crisis.