BACKGROUND: Elderly patients have been either excluded or underrepresented in acute myocardial infarction (AMI) clinical trials. To understand the impact of age on treatment, outcomes and complications, we analyzed the largest group of patients 75 years or older with AMI from registry. METHODS: We analyzed data from 14885 patients in the Korea Acute Myocardial Infarction Registry (KAMIR) between October 2005 and June 2008. Patients with AMI were divided into two groups: those ��� 75 years (n=2,506) and those < 75 years (n=10,160). The main clinical outcomes were 1-year major adverse cardiovascular events (MACE) and bleeding after primary percutaneous coronary intervention (PPCI). RESULTS: Elderly patients had higher rates of hypertension, diabetes and previous ischemic heart disease and less angiographic success after PPCI. There were less use of short-term adjunctive medications and antiplatelet agents in elderly compared with younger patients. However, major bleeding rate was higher in the elderly group (0.4% vs. 0.8%, p=0.01). In elderly patents, 1-year MACE (10.1% vs. 22.0%, p<0.001) and mortality rate (5.6% vs. 18.5%, p<0.001) were found to be higher. After multivariable adjustment, age was the strongest independent predictor of 1-year MACE (odds ratio [OR] = 1.753, 95% confidence interval [CI] = 1.316-2.333, p<0.001) and 1-year mortality (OR = 4.844, 95% CI = 3.551-6.608, p<0.001). CONCLUSIONS: Elderly patients were treated with less antiplatelet agents and had higher rates of major bleeding, 1-year MACE and mortality. Age with 75 years or older is the strongest predictor of 1-year MACE and mortality in AMI patients undergoing PPCI in this analysis. Therefore, a thorough understanding of the prognosis and a cautious approach in management of the elderly patients with AMI are needed.