Objective: To investigate the risk factors, clinical characteristics and coronary angiographic features in patients younger than 40 years with acute myocardial infarction(AMI). Methods: We collected data of patients with AMI from January 1999 to January 2009. Baseline clinical characteristics and coronary anatomy were compared between young (≤40 y) and older patients(60~75 y). Results: There were 106 cases in the young group and 112 cases in the older group. ST segment elevated myocardial infarction(STEMI) was presented in 91.5% patients of the young group, who were predominantly male,more likely to smoke, drinking, have higher coronary heart disease family history positive rate,and higher triglyceride(TG) levels,compared to older patients. Also,patients in the young group had less hypertension history and diabetic history, had lower pulse pressure and fasting blood glucose. The young group had higher rates of coronary angiography(64.2% vs. 40.2%,P < 0.05). Young patients were more likely to have single-vessel disease(58.82% vs. 13.33%,P < 0.05).Analysis of coronary angiogram also showed that the left anterior descending artery was the most commonly involved infarct related artery(56.63% vs. 32.29%,P < 0.01), no left main artery was involved in young group(0 vs. 10.42%, P < 0.01). Genisini scores were lower in young patients compared to the older group(23.69±22.80 vs. 39.21±40.37, P < 0.05). Multiple linear regression analysis showed that history of hypertension, Lp(a) and smoking index were independent influent factors for genisini scores in young patients with AMI. Conclusion:Smoking, drinking, family history and high TG were major risk factors for AMI in young who had less coronary pathological change, but strengthen the health education and improve the lifestyle such as hypertension control and smoking cessation should be strengthen to reduce the incidence of AMI in youngs.