A 69-year-old woman with Sheehan's syndrome who suffered acute Stanford type A aortic dissection had received corticosteroids and thyroid hormones for over 20 years. The entire ascending aorta was replaced in emergency graft replacement. We administered twice the usual dose of methylprednisolone during cardiopulmonary bypass and twice the patient's usual dose of prednisolone from postoperative day 1 to 6. The usual 100 micrograms of levothyroxine sodium was given orally from postoperative day 1. The patient's postoperative course was uneventful. This case emphasizes the importance of early active supplementary treatment with steroids and thyroid hormones for major surgery in patients with Sheehan's syndrome.