Excessive estrogenic influence is known to be associated with initiation/promotion of endometrial cancer (EC). Allelic polymorphisms of the genes involved in steroidogenesis/steroid metabolism may contribute to EC susceptibility. It is important to know endocrine mechanisms by which such susceptibility is acquired. Here, we compared CYP19 (aromatase) and CYP17 (17alpha-hydroxylase/17,20-lyase) gene polymorphisms correspondingly in 136 and 165 EC patients and in 116 and 188 non-affected women primarily of postmenopausal age. In these expanded studies we confirmed our previous observations that genotypes with longest alleles of CYP19 (A6 or A7) are over-represented (64.7+/-4.0 vs. 49.1+/-4.6%, P = 0.04, and 11.0+/-2.7 vs. 1.7+/-1.2%, P = 0.01)) and A2/A2 CYP17 genotype is under-represented (12.1+/-2.5 vs. 25.0+/-3.2%, P = 0.001) in patients as compared to controls. Additionally, aromatase activity was studied by tritiated water release assay in tumor tissues of 32 EC patients. In carriers of A2/A2 CYP17 genotype this activity was significantly lower than in carriers of A1/A1 genotype or in combined group of A1/A1 and A1/A2 CYP17 carriers (P = 0.04 in both cases). On the other side, intratumoral aromatase activity demonstrated tendency to higher values in carriers of longest CYP19 alleles (A6A6 and A6A7) than in carriers of all other CYP19 allele variants (P = 0.066). Thus, specific set of genetic polymorphisms (carrying of CYP17 A1 allele and combination of longest A6 or A7 CYP19 alleles) may predispose to the induction of higher rate of local estrogen biosynthesis in malignant endometrium, that in its turn may support growth of the latter. Further studies are warranted to connect revealed regularities with the type I or II of EC.