The objective was to investigate the immunohistochemical expression of p27, cyclin E, and CDK2 in normal and cancerous endometrium. Expression of p27 in premenopausal normal endometrium was significantly higher than that in postmenopausal normal endometrium (p=0.019). A significantly lower amount of p27 staining was observed in endometrial cancer tissues from premenopausal women than in normal premenopausal endometrium (p=0.015). Cyclin E expression in premenopausal normal endometrium was significantly higher than that in postmenopausal normal endometrium (p=0.003). A significantly higher amount of cyclin E staining was observed in endometrial cancer tissues from postmenopausal women than in normal postmenopausal endometrium (p=0.017). Regarding menopausal status, no significant difference in CDK2 staining was observed between cancerous and normal endometrium. There was a positive significant correlation between cyclin E and CDK2 expression levels in endometrial cancers (p<0.05). Western blot analysis confirmed elevated p27 protein levels in samples with positive p27 immunostaining. Considerable levels of p27 mRNA were detected in all normal and cancerous samples examined by semi-quantitative PCR. No significant relationship was found between telomerase activity and its association with p27 and cyclin E expression in endometrial cancers. These findings suggested that the decreased expression of p27 caused by post-translational mechanism might play an important role in endometrial cancer development in premenopausal women. In addition, increased cyclin E expression may play an important role in endometrial cancer development in postmenopausal women.