Myxedema coma, an extreme expression of hypothyroidism, represents a medical emergency with high mortality. Hypothermia and cerebro-vascular accidents should be taken into account for correct differential diagnosis. The treatment of myxedema coma is based on prevention of the precipitating factors and on the administration of generous doses of L-thyroxine and/or triiodothyronine, associated with steroids and drugs for respiratory and cardio-vascular complications.