A patient presented with hyperthyroidism and a thyroid swelling, clini
cally thought to be malignant. Fine-needle aspiration of the thyroid n
odule revealed microfilariae of Wuchereria bancrofti. After therapy th
e thyroid swelling subsided and the patient became euthyroid The possi
ble etiologic role of microfilariae in the genesis of the thyroid tumo
r and hyperthyroidism is discussed. (C) 1997 Wiley-Liss, Inc.