Because grotesque swelling of lower and upper extremities occurs in less than 3% of patients with myxedema, it has been proposed that the development of this rare dermopathy requires both severity and a long duration of active autoinumme disease. It is speculated that the deposition of mucopolysaccharides causes clinical manifestations in areas exposed to trauma or mechanical factors. We report a case of severe elephantiasic myxedema in a 68-year-old black man that remained undiagnosed for 3 years. His first symptoms were hard swelling of feet and the pretibial areas that then spread to his hands and forearms causing marked impairment of movement. Physical examination revealed bilateral breast enlargement, periorbital edema, and proptosis. Skin biopsies showed large deposits of mucin in the superficial and medium dermis of the legs and breast. Thyroid function tests revealed a suppressed thyroid-stimulating hormone of 0.04 mU/L with normal free T4,1.46 ng/dL, that remained unchanged for 4 months. Antithyroid-stimulating hormone receptor antibodies were markedly positive: thyrotropinreceptor antibody, 520 U/L (positive > 15). The patient lost 15 kg over the next 8 months without treatment, and armodarone was then introduced because of increasing cardiac arrhythmias. This led to overt hypothyroidism (thyroid-stimulating hormone, 15.3 mU/L). The development of severe elephantiasic myxedema during the subclinical phase of the autoimmune thyroid disease suggests that high levels of thyrotropin-receptor antibody are important in the genesis of glycosaminoglycan production and accumulation.165245247