Over a period of 25 years (1961-1986), 30 consecutive patients were operated upon for solitary "HOT" nodules. The autonomy of these nodules was substantiated by cytomel nonsuppressibility on 131I or 123I scanning, or TSH stimulated enhancement of the remaining suppressed thyroid tissue (n = 24); or as a solitary toxic hot nodule with suppression of the remaining thyroid tissue (n = 6). Seventeen of these patients were euthyroid and 13 were thyrotoxic and required preoperative preparation with antithyroid medication. Five patients had a history of head and neck irradiation. The population consisted of 24 women and six men. Their ages ranged from 14 to 68 years. The tumors ranged in size from 1.5 to 7 cm. The pathologic findings consisted of "colloid" adenoma in nine patients, follicular adenoma in 19 patients, and a follicular carcinoma in two patients, for an incidence of 6 per cent. It is of interest that neither of the patients with thyroid carcinoma were toxic or had a history of radiation exposure. These findings support the concept that the incidence of carcinoma in truly autonomous "HOT" thyroid nodules is not negligible.