Genetic variations of genes encoding the endothelial nitric oxide synthase (eNOS) and the NADH/NADPH oxidase system are related with atherosclerosis in the general population, but their significance in women is not sufficiently assessed. We investigated the potential association between the G894T polymorphism of the NOS3 gene and the C242T polymorphism of the CYBA gene with subclinical vascular disease. Seventy (70) healthy, normally ovulating, premenopausal women were recruited for this study. Venous blood samples were obtained for biochemical/hormonal assessment as well as for genotyping, using real-time PCR. Sonographically assessed indices of vascular structure and function included carotid and femoral intima-media thickness (IMT), flow-mediated dilation (FMD), carotid-femoral pulse-wave velocity (PWV), and augmentation index. The prevalence of wild type, heterozygote, and homozygote genotype was 44.3% (31/70), 54.3% (38/70), and 1.4% (1/70) for the G894T polymorphism and 38.6% (27/70), 31.4% (22/70), and 30.0% (21/70) for the C242T polymorphism, respectively. After multivariable adjustment, the hC242T polymorphism was a predictor of both internal carotid IMT (b-coefficient - 0.119, p = 0.011) and combined-IMT (b-coefficient - 0.061, p = 0.015). Systolic blood pressure, lipids, and hC242T determined values of FMD (b-coefficient - 1.604, p = 0.034). Concerning the NOS3 G894T polymorphism, carriers of the polymorphic variant had higher values of IMT and PWV compared to the wild-type subgroup (carotid bulb-IMT and PWV, heterozygotes/homozygotes vs wild type 0.7 ± 0.2 vs 0.6 ± 0.1 mm; 7.1 ± 0.8 vs 6.6 ± 0.7 m/s; p = 0.048 and p = 0.029, respectively). These differences, however, were rendered non-significant in the multivariable analysis. In healthy premenopausal women, the CYBA C242T polymorphism is an independent determinant of endothelial function and subclinical atherosclerosis of the carotid arteries. The NOS3 G894T polymorphic variant also correlated with atherosclerosis, an association probably mediated by the traditional risk factors for CVD. The relevance of these findings in the clinical setting remains to be elucidated.