['Factors related to malignant transformation of laryngeal precancerous lesions remain largely unknown, so we investigated the relationship between the expression of p27 and precancerous laryngeal lesion.', 'In this study we investigated the expressions of p27 and p53 protein in 56 cases with laryngeal precancerous or cancer lesions (20 cases of hyperplasia, 19 of dysplasia, and 17 of squamous cell carcinoma), and went on to evaluate the relationship between immunoreactivity of each of them and the histological findings. We also evaluated the correlation between immunoreactivity and proliferative activity with the aid of Ki-67 nuclear antigen staining.', 'A retrospective study was performed in 56 cases (20 with epithelial hyperplasia, 19 with epithelial dysplasia and 17 with laryngeal cancer). Immunohistochemistry was performed to investigate expression of p27, p53 protein and Ki-67 nuclear antigen staining, using the avidian-biotin-peroxidase complex technique.', 'p27 immunostaining was observed in 12 out of 20 cases of hyperplasia (60%), six out of 19 cases of dysplasia (31%), and 2/17 (12%) of carcinoma. We found significant association between p27 immunostaining and the histological findings. On the other hand, p53 immunostaining was observed in 6/20 (30%) of hyperplasia, 3/19 (16%) of dysplasia, and 7/17 (41%) of carcinoma. No significant association was found between p53 and the histological findings.'] Is reduced expression of p27 correlated with progression in precancerous lesions of the larynx?