We report a 59-year-old woman who had Hashimoto's thyroiditis (HT) with hypothyroidism. A solid hypervascularized nodule in the right lobe was detected by color flow doppler sonography (CFDS). Thyroid (99m)Tc pertechnetate scintigraphy revealed a hot area in the right lobe. After three months, thyroid function tests also revealed hypothyroidism and (131)I scintigraphy was similar to the previous scintigraphy. No nodular or hypervascularized lesion in the right lobe could be identified at the sixth month of L-T4 substitution therapy. In conclusion, HT may present as a single hot nodule and hypothyroidism. Imaging findings of HT should be carefully evaluated for the precise diagnosis.