Podoplanin, a transmembrane glycoprotein, has been considered to be expressed specifically by lymphatic endothelial cells. However, recent studies have shown that the protein is expressed in a variety of normal as well as neoplastic tissues, and that its expression might be related to cell migration and invasion. In this study, we examined podoplanin expression in inflamed gingival tissues using an immunohistochemical method. Positive immunoreactivity for podoplanin was found in the cell membrane and cytoplasm of basal cells of oral gingival epithelium when severe inflammatory cell infiltration was present in the connective tissue just under the epithelium. When inflammatory changes were weak or absent, little or no reactivity for podoplanin in the basal cells was observed. Positive reactivity for podoplanin was also detected in basal cell extensions. Surprisingly, strong immunoreactivity for podoplanin was observed in all layers of oral sulcular and junctional epithelia associated with severe inflammatory reaction in the connective tissue. These findings suggest that increased expression of podoplanin in gingival epithelium is related to the progression of chronic periodontitis.