Endometrioid and serous carcinomas of the endometrium differ dramatically in their pathogeny and clinical behaviour. CyclinD1 is critical for the G1/S part of the cell cycle. Cyclin D1 is often overexpressed in human neoplasias, by genes rearrangements, amplifications and mutations. Ki-67 is a cell proliferation marker that is positive in all phases of the cell cycle except Go. The purpose of this study was to compare endometrial carcinomas with endometrial hyperplasias, regarding their activity for cyclin D1 and Ki-67. Immunostains with Ki-67 and cyclin D1 antibodies were performed on formalin-fixed and paraffin-embedded tissue sections from 15 cases: 10 endometrial carcinomas, endometrioid and serous papillary, and 5 simple and complex hyperplasias, with and without cytologic atypia. Ki-67 was positive in all proliferative and neoplastic endometria. It is emphasized that the association of the cyclin D1 expression with the clinical aggressiveness is possible, but insufficient proved by now. Overexpression of cyclin D1 increases from normal endometrium to hyperplasia and carcinoma, suggesting that it may play a role in endometrial carcinogenesis.