Objectives Myxedema crisis, a fatal complication of severe hypothyroidism, is extremely rare in children and treatment guidelines are lacking. Since availability of intravenous levothyroxine is limited in resource poor settings, myxedema crisis can be treated with oral levothyroxine and/or oral liothyronine (if necessary), in the absence of cardiac risk factors, thus hastening the recovery and significantly decreasing the associated morbidity and mortality. In the background of untreated hypothyroidism, a possible association of ovarian hyperstimulation syndrome (OHSS) and reactive pituitary hyperplasia should be kept in mind, thus preventing unnecessary interventions. Case presentation A 13-year-old girl child with Down syndrome, presented with myxedema crisis, as initial presentation of untreated hypothyroidism. Conclusions Annual screening, timely diagnosis of hypothyroidism, and early initiation of thyroid hormone supplementation will prevent associated physical and neurocognitive morbidity in children, especially those with Down syndrome. Importance of oral liothyronine supplementation in myxedema crisis, has been highlighted in this case report.