Myotonic dystrophy is the most common and serious form of myotonic disease. It is a multisystem disease, although skeletal muscles are principally affected. Its most common complication is postoperative respiratory failure. We report such a case in a patient undergoing total abdominal hysterectomy after inhalational anesthesia. The patient had preoperative muscular weakness, which was, we concluded, induced by hypothyroidism and an old lacunar infarction in left thalamus with mild cerebral atrophy by preoperative thyroid function testing and brain CT. We studied electromyographic results and more intensively queried family history after postoperative respiratory failure. It was confirmed that the patient had myotonic dystrophy.