Purpose of investigation: This study aimed to investigate the immunohistochemical expression of cyclins Dl and E in normal, hyperplastic and neoplastic endometrium, and their correlation with proliferative activity and clinicopathological features. Methods: We carried out immunohistochemical techniques on archived material of formalin-fixed paraffin-embedded tissues using the antibodies against the cyclins Dl and E, PR-ER, p53, Ki67 (MIBl) and pRb with the streptavidin-biotin-peroxidase method in a total of 20 cases of normal endometrium, 32 cases of hyperplastic endometrium and 66 cases of endometrial carcinomas. Results: Cyclin DI and E immunoreactivity was observed in the nuclei of tumour cells in 18.2% and 39.1 %, respectively, of the cases of endometrial carcinomas. Cyclin DI labelling index was not significantly correlated with any of the clinicopathologic para­meters examined. However, there was a significant correlation between the cyclin E labelling index and histological grade of car­cinoma (p = 0.00096), which increased significantly with histological grades of malignancy. We also detected a significant correla­tion between cyclin E and PCNA (p < 0.0001) as well as with the tumor suppressor genes p53 and pRb (p = 0.052 and 0.0002, respectively) in endometrioid endometrial carcinoma. Conclusion: Our results indicate that cyclin E overexpression may be involved in the development and/or proliferation and dif­ferentiation of human endometrioid endometrial carcinoma. lmmunoexpression of cyclin D1 does not appear to be associated with cell-cycle progression in the benign or malignant endometrium.