Untreated or unrecognized hypothyroidism may progress to severe decompensated hypothyroidism or myxedema coma. Relatively few cases are reported in the literature since the first case was apparently reported from the St. Thomas Hospital in London in 1879. The paucity of cases may be due to either underreporting or improvement in the diagnosis and treatment of uncomplicated hypothyroidism. However, despite the ready availability of sensitive thyrotropin assays, the recognition and treatment of myxedema coma remains a challenge. Although thyroid hormone treatment is highly effective when combined with ventilatory and hemodynamic support in the intensive care unit setting, controversies abound on the optimal and most effective choice of thyroid hormone preparation: thyroxine and triiodothyronine and in what amount. Accumulated evidence now shows that proper use of either thyroxine alone or in combination with triiodothyronine may be effective therapy.