A 56-year-old woman, who had not received medical care for 30 years, presented to the emergency department with progressively worsening fatigue and confusion. On physical examination, she was disoriented but conversant. Vital signs were notable for hypothermia (temperature, 34°C [93°F]), a heart rate of 50 beats per minute, and a respiratory rate of 12 breaths per minute. She had edema of the face (Panel A), coarse skin, thin hair, brittle nails, and nonpitting edema of the lower extremities (Panel B). Biochemical evaluation revealed a thyrotropin level of 258 mIU per liter (normal range, 0.4 to 4.2), a free thyroxine level of 0.1 ng per deciliter (1 pmol per liter; normal range, 0.8 to 2.2 ng per deciliter [10 to 28 pmol per liter]), and a serum sodium level of 130 mmol per liter (normal range, 136 to 146). These findings supported the diagnosis of myxedema. No clear cause of the patient's clinical deterioration was identified. She was admitted to the intensive care unit for intravenous repletion of thyroid hormone. Over the next several days, her vital signs and mental status returned to normal, and she was discharged to a rehabilitation center. Myxedema coma, unlike what the name suggests, does not require a comatose state for diagnosis. The condition is diagnosed from a combination of abnormal thyroid function, physical examination findings of severe hypothyroidism, and altered mental status. Bradycardia, hypothermia, and hyponatremia are often present as well. Treatment is often administered intravenously, since there may be edema of the gut wall that limits oral absorption. One year after thyroid hormone repletion and the normalization of thyroid function, the patient had dramatic improvement of skin findings (Panels C and D).