Many studies have shown a close correlation between intima-medial thickness of the carotid artery measured by high resolution ultrasonography and the presence of coronary artery disease or atherogenic risk factors. However, reference values for the value of intima-medial thickness (IMT) in healthy subjects have not yet been established. The aim of this study was, therefore, to determine the reference values of carotid (C-IMT) and femoral intima-medial thickness (F-IMT) with respect to age and gender in healthy subjects (53 women and 45 men) aged 20 to 60, with no family or personal history of cardiovascular disease or atherogenic risk factors, underwent high resolution colour echo-Doppler examination. The mean C-IMT was 556 +/- 57 microns in women and 573 +/- 70 microns in men (NS), and the femoral equivalent was 543 +/- 63 microns in women and 562 +/- 74 microns in men (NS). Between the ages of 20 and 60, the C-IMT increased by 1.8 microns per year (p < 0.03) in women and 3.4 microns (p < 0.001) in men, the variations being respectively 1.2 microns (NS) and 3.1 microns (p < 0.002) in the femoral artery. Multiple regression analysis including gender and individual values of age, body mass index and lipid profile confirmed that only age was significantly correlated to the increase in thickness. The authors conclude that the reference values of IMT do not differ with gender or site of analysis, but there is a slight influence with respect to age.