BACKGROUND AND OBJECTIVES: The effectiveness of adjunct balloon dilation after drug-eluting stent (DES) deployment has not been sufficiently evaluated. We evaluated whether adjunct balloon dilation was associated with a reduction in major adverse cardiac events (MACEs) after long everolimus-eluting stents (EESs) implantation. SUBJECTS AND METHODS: Drawing from 2 randomized trials, a total of 1,672 patients treated with long EES were analyzed. Of 1,672 patients, 1,061 patients (64%) received post-stent adjunct balloon dilation. MACE, defined as a composite of cardiac death, myocardial infarction, and target-lesion revascularization (TLR), was compared between patients who received post-stent adjunct balloon dilation and patients who did not in 595 propensity score-matched pairs. RESULTS: For the matched population, MACE occurred in 29 patients (4.9%) who received adjunct balloon dilation and in 29 patients (4.9%) who did not (hazard ratio [HR], 1.01; 95% confidence interval [CI], 0.60–1.69; p=0.972). However, significant interactions were observed among the subgroups for clinical presentation and vessel size. Adjunct balloon dilation was more favored within the subset of patients with stable angina vs. the subset of patients with acute coronary syndrome (p for interaction=0.037), and within the subset of lesions with small vessel diameter (reference vessel diameter [RVD] <3 mm) vs. the subset of lesions with larger vessel diameter (RVD ≥3 mm; p for interaction=0.027). CONCLUSION: Adjunct balloon dilation was not associated with MACE reduction at 1 year among patients requiring long EES implantation. However, post-stent adjunct balloon dilation may be necessary for patients requiring long EES implantation who present with stable angina or for lesions with small vessel diameters.