Apoptosis plays one of the major roles in the progression of human cancers including cervical carcinoma. The aim of our study was to analyse the expression of Cas3, Bax and their correlation with the proliferation index and ER expression status during the progression of cervical intraepithelial neoplasia (CIN). Study included altogether 140 specimens, divided into two major groups, such as: cervical lesions without co-infections and with co-infections. Standard immunohistochemistry was used to detect antigens: Ki67, Cas3, Bax and ER. The study results showed that the expression of Cas3 is significantly decreased whilst the expression of Bax is significantly increased during the progression of CIN in both groups with and without co-infections. The expression of Bax negatively correlates with the expression of Cas3 (r=-42.4, p<0.05) and ER (r=-33.4, p<0.05) and positively correlates with the expression of proliferation marker Ki67 (r=56.3, p<0.05). The results indicate that the deregulated apoptosis measured as increased expression of Bax and Cas3 loss, as well as the increase in proliferation index measured as Ki67 expression is significantly related to the progression of CIN into cervical carcinoma. Therefore, the measuring of mentioned protein expression could be used as the markers of the CIN progression.