Background: Plaque prolapse (PP) has been reported to be 15 to 20% of cases after stenting and has a benign course at long-term follow-up. However, the influence of PP after stenting in STEMI patients has yet to be investigated. The aim of this study was to evaluate the incidence and long-term outcomes of PP after BMS and DES implantation in patients undergoing primary PCI. Methods: The study population consisted of 53 BMS (51 patients) and 87 DES (84 patients) cases undergoing interventional IVUS examination after primary PCI. PP was defined as an intraluminal tissue (thrombus or atheroma) through the stent strut observed by IVUS. Patients were divided into two groups according to the presence/absence of PP. Cumulative incidence of major adverse cardiac events (MACE) including death, MI, and TLR and stent thrombosis (ST) were evaluated at 1 year after index procedure. Results: There was a 44.3% (62/140) incidence of PP after primary PCI. PP was frequently observed in RCA lesion and presence of intracoronary thrombus by coronary angiography (all for p<0.05). The rates of MACE and ST were not different between the 2 groups at 1-month and 1-year follow-up (all for P=NS) (Table). By multivariate analysis, RCA lesion was the only independent predictor of PP. Conclusion: The incidence of PP after primary PCI was high. The presence/absence of PP was not found to affect short- and long-term clinical outcomes in this patient subset.