OBJECTIVE: The purpose of this study is to compare the expression rate of cyclooxygenase-2 (COX-2), p53 in endometrial hyperplasia, endometrial cancer and normal endometrium and to correlate COX-2 with the clinicopathological factors and p53 in endometrial cancer. METHODS: Immunohistochemical stain of COX-2, p53 was performed on samples from a series of 19 cases of normal proliferative endometrium, 20 cases of complex endometrial hyperplasia and 19 cases of endometrial cancer. And then we analyzed the expression of COX-2 correlated the findings with clinicopathological factors and p53. Expression of COX-2 was scored according to the proportion of positive-staining cells: negative, no staining; 1+, <10%; 2+, 10-50%; 3+, >50. For p53 overexpression, when there were at least 10% of tumor cells stained, it was considered as positive. RESULTS: Overexpression of COX-2 (> or =2+) was seen in 5 (26.3%) of the endometrial cancers, 6 (30%) of the complex endometrial hyperplasia, and 4 (21.1%) of the normal endometria. The expression rates of COX-2 in endometrial cancer, hyperplasia and normal endometrium were not different statistically significant (p=0.93). COX-2 was not correlated with clinicopathological factors but correlated with p53 significantly (p=0.021). CONCLUSION: In this study, the immunohistochemical analysis showed no difference statistically in COX-2 expression between endometrial cancer and hyperplasia compared to normal endometria. COX-2 was significantly correlated with p53. This finding may represent that tumor suppressor p53 upregulates COX-2 expression.