To investigate intravascular ultrasound predictors of long-term clinical outcome in patients with acute coronary syndrome, 94 patients with a first acute coronary syndrome with both preintervention intravascular ultrasound imaging and long-term follow-up were enrolled in this study. Remodeling index was defined as external elastic membrane cross-sectional area at the target lesion divided by that at the proximal reference. Arterial remodeling was defined as either positive (PR: remodeling index >1.05) or intermediate/negative remodeling (remodeling index < or =1.05). Clinical events were death, myocardial infarction, and target-lesion revascularization. Patients were followed up for a mean of 3 years. PR was observed in 50 (53%), and intermediate/negative remodeling, in 44 (47%). During the 3-year follow-up, there were 20 target-lesion revascularization events and 5 deaths (2 cardiac and 3 noncardiac), but no myocardial infarctions. Patients with PR showed significantly lower major adverse cardiac event (MACE; death, myocardial infarction, and target-lesion revascularization)-free survival (log-rank p = 0.03). However, patients with plaque rupture showed a nonsignificant trend toward lower MACE-free survival (p = 0.13), but there were no significant differences in MACE-free survival between those with single versus multiple plaque ruptures. Using multivariate logistic regression analysis, only culprit lesion PR was an independent predictor of MACEs (p = 0.04). In conclusion, culprit-lesion remodeling rather than the presence or absence of culprit-lesion plaque rupture was a strong predictor of long-term (3-year) clinical outcome in patients with acute coronary syndrome.