BACKGROUND: A number of studies in western countries have shown that coronary artery disease(CAD) and younger patients with acute myocardial infarction(AMI) is less extensive but more. closely related to cigarette smoking. However, there are some similarities between the characteristics of the CAD and the risk factors analyzed by age subsets in patients with AMI in Korea. METHODS: Pre-discharge coronary angiograms and risk factors in 194 patients with first AMI(male/female : 154/40,79.4%/20.6%) were analyzed. A comparison was made between the lesion characteristics of the infarct related artery(IRA) and the CAD risk factors. Those under 49 years old (Group I, n=54, male/female : 50/4 : 92.6%/7.4%) and those over 50 years old ( Group II, n=140, male/female : 104/36 : 74.3%/25.7%). RESULTS: There are 54 and 140 patients in groups I and II respectively. 92% of group I and 74.1% of group II were male (p<0.01). At the time of study, more group I patients were smoking cigarettes and drinking alcohol(over 3 times per week 22.6% vs 11.5%, p<0.01) and insignificant stenosis was more common in group I than in group II. In both groups, the most common IRA was the left anterior descending artery and concurrently the anterior wall was the most common morphological type of coronary stenosis of IRA was concentric irregular in group I(27.7%) and eccentric smooth in groupII(31.5%). Although group I had the larger minimal cross sectional area of coronary stenosis(0.97+/-1.16mm2 and 0.54+/-0.80mm2, respectively, p<0.05, reference diameters 2.71+/-0.60mm and 2.66+/-0.67mm, respectively),the coronary lesion was shorter in group I patients(3.39+/-4.06cm and 5.49+/-6.13cm respecitively, p=0.03). CONCLUSION: These findings reveal that coronary atherosclerotic lesions of IRA in patients with AMI in the younger age group are less severe. However, they are more closely related to cigarette smoking and alcohol intake, than cases in the older age group.