Background: Recently the number of young patients with acute myocardial infarction (AMI) has been increased in Korea. Methods: A total of 3,252 patients with AMI were included in Korean acute myocardial infarction registry (KAMIR) between October 2005 and May 2007. Risk factor was retrospectively compared in 279 young patients <40 years (Group I), and 2,972 old patients (70-80 year-old, Group 2). There was 261(80%) men in the Group I and 1,500 (50.5%) men in the group II. Male was more common in young age group (p=0.0001). Clinical follow-up was performed in the 134 patients (48%) in Group I and 1,567 patients(52.7%) in Group II. Results : The incidence of STEMI was higher in Group I [n=190 (68%) vs. 1622(54%),p=0.000). The Group I had higher prevalence of smoking, dyslipidemia, and family history [n=234 (83.9%) vs. 1164 (39.2%), p=0.0001 and n=32 (11%) vs. 173(5.8%), p=0.0001 and n=51 (18.3%) vs. 97 (3.3%) p=0.0001]. The Group I had lower prevalence of hypertension and diabetes, and history of ischemic heart disease [n=78 (28%) vs. 1646 (55.4%), p=0.0001 and n=33 (11.8%) vs. 864 (29.1%), p=0.0001 and n=24 (8.6%) vs. 596 (20.0%) p=0.0001]. The lipid profile except for HDL-cholesterol in Group I was higher than Group II; total cholesterol 194.4짹50.8 vs. 176.9짹47.6 mg/dL p=0.0001, triglyceride 195.6짹240 108.0짹79.7 mg/dL p=0.0001, HDL-cholesterol 43.8짹10.2 vs. 46.1짹25.4 mg/dL, p=0.149, LDL-cholesterol 123.3짹55.3 vs. 113.0짹45.0 mg/dL, p=0.005). After 6-12 month clinical follow-up, the incidence of major adverse cardiac events (MACE) in Group I was lower than Group II [9(3.2%) vs. 194(6.5%) p=0.009]. Conclusion: In young Korean patients with AMI, smoking, dyslipidemia and family history was more frequently associated with AMI. The short-term clinical prognosis in the young patients with AMI was better than in old patients.