Background: Little is known about the predictors for progression of non-culprit coronary artery atherosclerosis after percutaneous coronary intervention (PCI) for culprit coronary artery in patients with acute myocardial infarction (AMI). Methods: Between November 2005 and January 2008, 14,871 patients suspected AMI were included from the Korea AMI Registry, and 6,574 patients (4,847 men; mean age = 61.6 짹 12.0 years-old) underwent PCI and followed up 1-year were finally analyzed. Those who underwent nontarget lesion revascularization (non-TLR) were compared with those who did not. Results: Of these patients, 217 (3.4%) required a non-TLR at 1 year. The median time from the first to the second PCI was 196 days (interquartile range 4 to 357). Kaplan-Meier analysis of non-TLR PCI at 1 year according to initial degree of coronary artery disease is shown in figure. In multivariate logistic regression model, patients with multivessel coronary artery disease during first PCI (adjusted odds ratio [OR] 2.330, 95% confidence interval [CI] 1.585 to 3.426 for 2 vessels, p<0.001; adjusted OR 4.499, 95% CI 3.101 to 6.527 for 3 vessels, p<0.001) in addition to previous history of MI (adjusted OR 1.915, 95% CI 1.008 to 3.636; p=0.047), pre-TIMI flow 0 (adjusted OR 1.356, 95% CI 1.020 to 1.802; p=0.036), and post-TIMI flow 3 (adjusted OR 0.517, 95% CI 0.296 to 0.902; p=0.020) were Independent predictors of need for non-TLR after adjustment for confounding variables. Conclusion: Greater coronary artery disease burden confers a significantly higher risk for clinical plaque progression. Aggressive preventive and medical management should be applied to post-MI patients with multivessel coronary artery disease for prevention of these subsequent events.