BACKGROUND AND OBJECTIVES: The goal of this study is to investigate alterations of cell-cycle-related molecules, including p53, p21, cyclin D1 and Ki-67, in tumors arising in the sinonasal region. MATERIALS AND METHODS: The study materials were 16 specimens of normal nasal mucosa, 16 inverted papillomas (IPs) and 12 sinonasal squamous cell carcinomas. The p53, p21, cyclin D1 and Ki-67 expression was assessed by immunohistochemical staining. RESULT: IP and squamous cell carcinoma showed significant increase in the expression of p53, cyclin D1 and Ki-67 than normal mucosa. The expression of p53, cyclin D1 and Ki-67 of the carcinoma was stronger than the IP. But, the p21 expression was not associated with the IP and carcinoma. CONCLUSION: Increased levels of p53, cyclin D1 and Ki-67 expression correlate with increased cell proliferation in the tumors of sinonasal regions. These findings indicate that p53, cyclin D1 and Ki-67 expression may be useful markers for the dysregulations of cell kinetics in the tumors of sinonasal region.