Background:Percutaneous coronary intervention(PCI)of an intermediate stenosis without evidence of ischemia is often performed,but its benefit is unproven. The aim of this study is to investigate the appropriateness of drug-eluting stent(DES)implantation in an intermediate stenotic coronary artery disease, guided by conventional angiography vs. fractional flow reserve(FFR).Methods:Two hundred seven patients scheduled for PCI of an intermediate stenosis were prospectively enrolled in this study at the eight interventional cardiology centers in Korea.All patients were randomly divided into two groups.Group 1(n=119)was FFR guided PCI group.Group 2(n=88)was routine PCI group.In the group 1, if FFR was ���0.75, patients were assigned to deferral(n=85).If FFR was <0.75, PCI was performed as planned(n=34).Clinical follow-up is planned for 2 years.Results:There were no differences in baseline clinical characteristics between the 2 groups.One month follow-up was obtained in 86.5% of the patients. Event-free survival at 1 month was not different between the 2 groups(group 1, 98% vs. group 2, 98.8%; p= 1.00).Six month follow-up at single center was available in 77.6%(n=59).Event-free survival at 6 month at single center was not different between the 2 groups(96.8% vs. 100%; p=1.00).Conclusions:One month and six month clinical outcomes after deferral of PCI of an intermediate coronary stenosis based on FFR ���0.75 are excellent. Long-term clinical follow-up should be needed to evaluate the efficacy and safety of deferral of PCI guided FFR with DES.