To ascertain reference values of carotid intima-media thickness (cIMT) in a middle and old-aged sample of the Spanish general population and to establish the 75(th) percentile above which it is necessary to control more strictly other cardiovascular risk factors. To determine cIMT values and the number of carotid plaques in age and sex subgroups, and whether there are differences between them.Lipids, apolipoproteins, number of carotid atherosclerotic plaques if any, and cIMT of both common carotid arteries were determined in 171 individuals, representative of the adult general population of Burgos (Spain).The median age of the patients was 63 years (interquartile range = 20) and the 75th percentile of carotid IMT was 0,88 mm and 0,81 mm in men and women, respectively. This study shows that the values of cIMT median increase with age and are higher in men than in women in all age groups, except in individuals over 74 years where cIMT median values are similar. The presence or absence of atherosclerotic plaques was not statistically different between men and women at different ages.This population study shows the reference values of cIMT in a middle and old-aged sample of the Spanish population and shows that age, male gender, systolic blood pressure (SBP) and personal history of coronary heart disease are the main determinants of increased cIMT.