Backgrounds: When stenting in the proximal stenoses with mild ostial involvement, few studies to directly compare the long-term outcomes of ostial coverage have been performed. Methods: We reviewed consecutive 59 patients with proximal part stenosis at any coronary arteries. Each lesion has a mild ostial lesion and a distal tandem severe stenosis. All patients underwent follow-up coronary angiography when the patient has chest pain and at 9 month to 1 year after index PCI. Primary outcome was restenosis at proximal edge of the stent. Results : For 29 patients ostiums were covered by stent (covered group, 49.2%), stent was not covered at ostium for 30 patients (uncovered group, 50.8%). All patients were implanted with sirolimus-eluting stent (n=34) or paclitaxel eluting stent (n=25) (57.6% vs 42.4%). There was no difference with baseline characteristics between covered group and uncovered group. After follow-up period (387짹263 days), 7 patients developed restenosis in uncovered group, 1 patient did in covered group (23.3% vs. 3.4%, p=0.026). Uncoverage of ostium was a single independent risk factor for proximal edge restenosis (Adjusted hazard ratio[HR] = 9.392, 95% confidence interval [CI] : 1.095 to 80.582, p=0.041). Of enrolled lesions, left anterior descending artery (LAD) was dominant (n=32, 54.2%). Proximal edge restenosis occurred in 5 patients with proximal stenosis at LAD and 3 patients with stenosis at right coronary artery (15.6% vs. 15%). Conclusion : Ostial coverage is very important to prevent proximal edge restenosis in patients with proximal severe stenosis with mild ostial involvement during PCI.