Survivin is a novel member of the apoptosis protein inhibitors, but according to previous reports, it is also significantly linked to cell proliferating activity. In this study, we investigated the expression of survivin in thyroid neoplasms. Survivin was only occasionally expressed in normal follicular cells, whereas in follicular and papillary carcinomas, about 20% of cases were positive for survivin. The incidence was significantly higher in advanced stage papillary carcinoma (p=0.0080) and papillary and follicular carcinomas with poorly differentiated lesions (p=0.0150). In anaplastic carcinoma, survivin positivity was observed in 84% of the cases, which was in significantly higher incidence than in papillary or follicular carcinoma (p<0.0001). These results suggest that survivin is strongly related to the dedifferentiation of thyroid carcinoma.