Overexpression of thymosin beta-10 (TB10) has been shown in rat thyroid transformed cell lines, and in human thyroid carcinoma tissues and cell lines. To investigate whether TB10 detection could be a valid tool in the diagnosis of human thyroid neoplasias, we extended the analysis of TB10 expression to a large number of thyroid hyperproliferative and neoplastic tissues using an immunohistochemical assay. Our analyses showed a TB10 positive staining in all human thyroid carcinomas particularly in the anaplastic histotypes, whereas no TB10 immunostaining was observed in normal thyroid, in adenomas and the majority of the goiters. These results suggest that the evaluation of TB10 gene expression may be considered a promising means of diagnosis of human thyroid hyperproliferative disorders.