Abstract: Objective: To investigate the risk factors and the coronary angiographic findings in young adults with acute myocardial infarction(AMI). Methods: The AMI patients under the age of 40 were defined as youth group(n=48) and those above 40 as midelderly group(n=50). The clinical data(risk factors and coronary angiographic findings) of both groups were collected and compared. Results: The incidence of AMI was 97.97% in the male patients in the youth group,while it was 82.00% in the mid-elderly group (P < 0.05). The youth group had a lower proportion of hypertension(19.00% vs 60.00%,P < 0.01),and a higher proportion of non-"three highs" (hypertension,diabetes mellitus,dyslipidemia) (67.00% vs 30.00%,P < 0.01) as compared with the mid-elderly group. The proportion of patients with smoking as the only risk factor accounted for 52.00% in the youth group,while it was only 6.00% in the mid-elderly group. Among the six AMI cases with no"three highs"or smoking history in the youth group,3 were proved to have a family history of early-attacking cardiovascular disease,1 had atheroembolism and 2 had unknown reasons. The youth group had a higher proportion of single coronary artery lesions(46.00% vs 20.00%,P < 0.01) and lower proportion of multiple branch lesions(52.00% vs 78.00%,P < 0.01) than the mid-elderly group. Conclusions: Most of the young AMI patients are male,presenting no"three highs"; smoking is usually the only risk factor. And the young patients who do not have"three highs"or smoke usually have a family history of early-attacking cardiovascular disease. Compared with the mid-elderly,most of the young AMI patients suffer from single coronary vessel disease.