Urokinase type plasminogen activator receptor (uPAR) plays an important role in cancer invasion and metastasis. However, the uPAR expression has been rarely investigated in thyroid carcinomas. The aim of this study was to evaluate the clinical relevance of uPAR in thyroid tumors.Samples included 53 benign tumors (follicular adenoma 34, Graves' disease 8, adenomatous goiter 7 and others 4) and 62 cancers (papillary thyroid cancer (PTC) 47, follicular TC (FTC) 5, medullary TC (MTC) 5 and anaplastic TC (ATC) 5). uPAR expression was prospectively investigated with a labeled streptavidin-biotin method using an anti-uPAR monoclonal antibody. Patients were classified into a low- and high-staining group according to the percentage of positive cells (cut-off value=10%).uPAR was more strongly expressed in thyroid cancers (35.5%) than benign tumors (7.5%). FTC had a significantly higher uPAR expression compared to follicular adenoma (p<0.01). The positivity of uPAR was as follows: PTC 36.2%, FTC 60%, MTC 0% and ATC 40%. In PTC, high uPAR expression was associated with poorly-differentiated PTC (p<0.01) while had a trend to develop more distant metastases than those with low uPAR expression (p=0.17, by the Kaplan-Meier method).This study has shown that uPAR expression might be useful for the discrimination between FTC and follicular adenoma and could possibly be used as a prognostic factor in PTC.