Two cases operated upon with the clinical diagnosis of unifocal autonomous functioning thyroid nodules (AFTN) are reported where the histological diagnosis revealed a well differentiated thyroid carcinoma (follicular, papillary) without metastasis. The pathogenesis of differentiated thyroid carcinomas in cases of AFTN may be coincident. Alternatively it may evolve from thyroid epithelial cells of the hot nodule, resulting in a "hot" well differentiated thyroid carcinoma. These cases show that under the clinical diagnosis of AFTN a differentiated thyroid carcinoma can be hidden occasionally.