Background: No-reflow phenomenon has been related to a poor clinical outcome after primary percutaneous intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI). The purpose of this study was to assess whether certain characteristic features detected by intravascular ultrasound (IVUS) are associated with the development of no-reflow phenomenon after primary PCI for STEMI. Methods: One hundred-two consecutive patients with STEMI who underwent IVUS-guided primary PCI within 24 hours of symptom onset were analyzed. No-reflow was defined as post-PCI Thrombolysis In Myocardial Infarction (TIMI) flow grade 0 to 2. Results: The no-reflow phenomenon was observed in 24 individuals (23.5%). Patients with no reflow had higher prevalence of hypertension (72.7% vs. 37.9%, p = 0.002), lower left ventricular ejection fraction (45% vs. 49%, p = 0.050) and frequent use of intra-aortic balloon pump (IABP, 36.4% vs. 10.3%, p = 0.006). In patients with no-reflow, a lipid pool-like image was more commonly found compared with patients with reflow (95.8% vs. 65.0%, p = 0.016). However, there were no significant differences in the presence of thrombus (70.8% vs. 82.9%, p = 0.198), eccentric plaque (20.8% vs. 36.8%, p = 0.146), plaque rupture (79.2% vs. 78.9%, p = 0.982) and positive vessel remodeling (66.7% vs. 71.1%, p = 0.683) in patients with no-reflow and reflow. Logistic regression analysis showed that a lipid-pool-like image on IVUS (OR 8.0, 95% CI 1.01 to 31.19, p = 0.045) was univariate predictor of no-reflow. Multivariate analysis identified that age at presentation (OR 5.8, 95% CI 1.60 to 21.38, p = 0.008) and use of IABP (OR 4.8, 95% CI 1.26 to 18.20, p = 0.022) were independent predictors of no-reflow phenomenon. Conclusions: These findings suggest that a lipid pool-like image on IVUS is associated with an increased incidence of no-reflow phenomenon during primary PCI for STEMI. Keywords: Acute myocardial infarction, No-reflow, Intravascular ultrasound