Background: p27(kip1), a universal cyclin-dependent kinase inhibitor, is a useful marker for predicting clinical aggressiveness with various human tumors. In this study, p27 expression was investigated in pleomorphic adenomas (PAs) and adenoid cystic carcinomas (ACCs) of minor salivary glands to evaluate its utility for differentiation purposes. At the same time, the correlation between p27 and ACC grading was evaluated. Materials & Methods: Clinicopathological features of 22 patients (11 ACCs, 11 PAs), including age, sex and size of tumor were obtained from medical records. Immunohistochemical staining with p27(kip1) was performed for each specimen and p27 labelling indices were determined with a computer-assisted image-analyzing system (CAS 200). Pearson’s correlation coefficient, Spearman’s correlation coefficient, Students t-test, Kruskal-Wallis test and ANOVA were applied for statistical analyses using SPSS 11.5. Results: p27 LIs for all PAs were above 25% whereas for ACCs they were under 25% (except one case). p27 expression (LI and intensity) was significantly lower in ACCs than PAs. The correlation between p27 expression and ACC grading was not significant. Conclusion: Overall, these findings suggest that reduced expression of p27 might be correlated with the development of ACC and could be an indicator of malignant behavior.