To investigate the relationship between the quantitative morphometric characteristics of intimal thickening and coronary atherosclerosis, 306 coronary arteries from 102 autopsied cases, 61 males and 41 females.aged 15 to 39 years (divided into 5 age groups), in Beijing were morphometrically studied.Methods By using an image analysis system, intimal and medial thickness was measured,intimal to medial thickness ratio, eccentricity index, luminal stenosis rate. and average annual increasing rate in intimal thickness were calculated.Results The intimal thickness increased with ageing.The intima was markedly thicker in males than in females of the same age group. Among the 3 coronary arteries[left anterior descending (LAD),right coronary (RC) .and left circumalex(LC) ]studied, the rate and degree of intimal thickening were most marked in the LAD and then the RC and LC. Intimal thickening increased more rapidly in the LAD in both sexes in the 20 ～24 years group with average annual increasing rates of 8. 6 % (males) and 9. 5% (females). The thickness then remained steady. However, a second peak of thickening of the LAD in the 35～39 years group in males with a average annual increasing rate of 9. 2% ,meanwhile the percentage of luminal stenosis was 57.4%. The average annual increasing rate of LAD was up to 3. 8% in females in the 30 to 34 y6ars group with no further increase in the 35～39 years group,but the percentage of luminal stenosis was <51 %. Two different types of thickening,namely diffused and eccentric,were found, the latter with characteristic features of atherosclerosis is prone to develop into atherosclerosis plague. The type of thickening of LAD which shows the highest prevalence of CHD clinically was eccentric.Conclusions Intimal thickening with ageing is a changing from physiological to pathological process and intimal thickening froms the structural base for atherosclerosis.