The p16 gene encodes an inhibitor of the cyclin-dependent kinase, which inactivates cyclin-dependent kinase and contro1s the cell cycle progression, The 10ss of p16 expression or overexpression has been reported in many kinds of tumors, Both p16 and PCNA regu1ates cell cycle progression at the Gl/8 checkpoint, Although many researches about the p16 expression in ora1 cancer have been carried out, there are few studies about the corre1ation between p16 ex pression and pro1iferation of ora1 cancer cells The object of this study was to eva1uate the avai1ability of p16 as ear1y diagnostic factor and prognostic factor through corre1atión ana1ysis of p16 expression in ora1 squamous cell carcinoma and its re1ation to PCNA index and clinicopatho1ogic factors 80 we investigated p16 immunohistochemica1 expression of 83 ora1 squmaous cell carcinomas, and obtained the resu1ts as followed, 18 out of the 83 cases(21, 69%) showed p16 positive and 65 samp1es(78,31%) showed p16 negative, Whi1e the mean va1ue of PCNA indices of p16 positive cases was 65,94 ::t 18,32, that of PCNA indices at p16 negati ve ones 54,79 ::t 18, 39, This difference between them showed statistica1 sígnificance, (P=O, 030) p16 positive group was 12/60(20, 0%) of well differentiated tumors and p16 negative group was 6/23(16, 1%) of moderate1y or poor1y differentiated tumors, This difference did not show statistica1 significance. (P=O. 372) From the resu1ts above, it was suggested p16 expression is re1ated to PCNA index in ora1 squamous cell carcinomas.