Different types of human papilloma virus are known to be closely associated with laryngeal papillomas. On the other hand, the proliferation of epithelial cells is associated with various abnormalities in the mechanisms of cellular regulation. In this study, we detected the expressions of p53, p21 and p27 proteins in adult-onset laryngeal papillomas by inummohistochemical techniques. The objective of this study is to evaluate the expression of these factors in adult-onset laryngeal papillomas and to determine whether such expression is correlated with the existence of dysplastic epithelium covering the papillomas. Eighteen patients with adult-onset papillomas who were surgically treated at the Department of Otolaryngology at the University of Istanbul between January 1994 and December 1999 were included in this study. Anti-p21, -p27 and -p53 antibodies were used to perform immunostaining. Positive nuclear staining for p2l was detected in 14 of the 18 (78%) cases, especially in the parabasal layer. Also, in 78% of the cases, weak to strong immunoreactivity was observed for p27. In all cases, negative immunoreactivity was observed for p53 throughout the epithelium except for the basal and parabasal cells. A negative correlation was observed between the existence of dysplastic epithelium and p21 expression (P=0.02). In conclusion, variable p21 and p27 expression was detected by immunohistochemistry in our series of 18 cases of adult-onset laryngeal papillomatosis, and a statistically significant inverse correlation was detected between p21 expression and the existence of dysplastic epithelium covering the papillomas. Further prospective studies are warranted to determine the prognostic values of these variables and to evaluate their role in the pathogenesis of adult-onset laryngeal papillomas.