Background: Fractional flow reserve (FFR) is a physiologic parameter that assesses the functional significance of a lesion. We performed this study to evaluate the outcomes of the FFR-guided intervention strategy in intermediate lesions. Methods: From Apr 2003 to Aug 2005, FFR was consecutively measured in 107 angiographic intermediate lesions (percent stenosis: 40-70% by visual estimation) at major epicardial braches (102 patients: age 63 years, male 67%). Patients with acute myocardial infarction (MI) and left ventricular dysfunction were excluded. FFR was measured using RADI 4 pressure wire and hyperemia was induced by both adenosine bolus administration (40-80ug) and continuous infusion (240ug/min). Lesions were divided into 2 groups according to FFR (group 1: FFR<0.75 (n=25), group 2: FFR>=0.75 (n=82)). One year clinical follow-up event (cardiac death, MI and target lesion revascularization (TLR)) rates were evaluated. Results: Mean percent stenosis, reference diameter and lesion length were 57짹12%, 2.8짹0.6mm and 22짹12mm, respectively. LAD was the most frequent (58%) lesion location and 91% were de novo lesions. There were no differences in baseline clinical characteristics between 2 groups Lesion length were longer in group 1 (31mm vs. 20mm, p=0.02). However there was no difference in percent stenosis (58짹12% vs. 57짹12%). Revascularization was performed in 64% of group 1 and it was deferred in 90% of group 2 lesions (P<0.001). During 1 year follow-up, MACE occurred in 12% of group 1 and 5% of group 2 lesions (P=0.2). One-year event rate of lesions which were not treated according to FFR was only 5.6%. The lesions treated by FFR guide (FFR<0.75 intervention, FFR>=0.75 defer) had only 5% event rate. However, MACE occurred in 12% (3/25) of lesions treated against FFR. Conclusion: Angiographic percent stenosis was not accurate in assessment of functional significance of intermediate lesions. Deferral of revascularization according to FFR seems to be safe and resulted in a relatively low event rate.