ObjectiveTo investigate whether the thickness of the layers of the carotid artery (externa, media, and intima) are affected by menopause and its treatment with hormone replacement therapy (HRT).MethodsOne hundred twenty-nine postmenopausal women were recruited sequentially and classified into three groups. Forty-six were taking oral HRT, 32 had estradiol implants, and 51 had never taken HRT. The three layers of the externa wall of the carotid artery were identified and measured by high-resolution ultrasound.ResultsWomen with implants had thicker carotid artery wall measurements (0.84 ± 0.26 mm) than the other groups. The media (0.32 ± 0.11 mm) was significantly thicker in the implant group. This layer has a high connective tissue component, including collagen type I, collagen type III, and elastin fibers. The intima layer was thinner (0.25 ± 0.09 mm) in the oral HRT group compared with controls (0.29 ± 0.1 mm). A statistically significant higher intima-media ratio (1.17 ± 0.05) was calculated for the control group, compared with both the oral HRT (0.92 ± 0.04) and implant groups (0.94 ± 0.03).ConclusionOur findings suggest that HRT given to postmenopausal women influences differentially the layers of the carotid artery. Hormones seem to encourage thickening of the layers with the highest connective tissue component (externa and media) and to delay thickening of the atheromatous intima layer. These effects on the vascular system may be partly responsible for the cardioprotection attributed to HRT.