Osteopontin (OPN) is a secreted, adhesive glycophosphoprotein that has been implicated in both normal and pathologic processes. In recent years, it has been suggested that OPN expression also plays an important role in tumorgenesis, tumor progression and tumor metastasis. To investigate OPN expression in papillary thyroid carcinoma, thirty paraffin sections of papillary thyroid carcinoma confirmed pathologically were examined by immunohistochemistry and in situ hybridization. Immunopositive reactions for OPN-protein were obtained in the nuclear and perinuclear area in all cases. OPN mRNA was expressed in the carcinoma cells around the microcalcifications. The results demonstrated that OPN mRNA is expressed not only by the infiltrated macrophages but also by the papillary thyroid cancer cells. Hence, OPN expression can be considered a pathological feature of papillary thyroid carcinoma and further study into the relation between OPN and the biological behavior of papillary thyroid carcinoma is warranted.