In this study, we demonstrated that (1) cdc25B and cdc25A were not overexpressed in normal thyroid tissue, (2) cdc25B was frequently overexpressed in follicular adenoma and minimally invasive follicular carcinoma, but the incidence significantly decreased in widely invasive follicular carcinoma, (3) the incidence of cdc25B overexpression significantly decreased with the dedifferentiation of carcinoma, and (4) cdc25A was frequently overexpressed in thyroid neoplasms regardless of their histological types. The gene discussed is CDC25B; the disease is carcinoma.