Objectives: Primary angioplasty has been suggested as a possible treatment for patients presenting with AMI and onset of chest pain>12h, but it remains unclear if an invasive strategy is beneficial to these patients. This study was designed to compare the early clinical outcome of patients presenting with >12h from onset of chest pain and acute ST elevation myocardial infarct who received either initial invasive or conservative therapy. Methods: We used Korean Acute Myocardial Infarction Registry (KAMIR) sponsored by The Korean Society of Circulation, to define a cohort of patients with STEMI. During the study period of November 2005 to January 2007, there were 8560 AMI patients in KAMIR. The final cohort included 904 STEMI patients presenting with >12 h. 320 STEMI patients were treated conservatively and 584 STEMI patients treated with primary PCI. In-hospital mortality and early outcome were compared on the basis of the initial therapy received. Differences between the two groups were evaluated with the Student t test and chi-square test. Results: Patients in invasive group were younger without significance, and more likely to have had a typical chest pain at arrival (p <0.01). There was no difference between medical histories. Although patients with invasive therapy were more likely to be in Killip class I (p<0.05), systolic BP and heart rate were similar between the two groups. 72% of the conservative group eventually underwent coronary angiography. There was no significant difference in the incidence of procedure complications. Patients with invasive therapy showed lower tendency (6.3% vs 7.5%) of unadjusted hospital mortality without significance. There was no significant difference in the rates of recurrent MI and death between the two groups at 6 months follow up (MACE ratio 4.3% vs 2.5%). Conclusions: Patients receiving early invasive therapy had lower risk features on presentation. Although the rate of in-hospital mortality remained lower in the invasive therapy group, there was no statistical difference in the early clinical outcome. Primary angioplasty may be beneficial in certain patients presenting late after onset of chest pain, but this hypothesis should be tested in a randomized trial.