The objective of this study was to examine the usefulness of fractional flow reserve (FFR) in determining the indication of target lesion revascularization (TLR) at follow-up angiography after percutaneous coronary intervention (PCI). One hundred forty-seven patients with 155 lesions that had intermediate restenosis took part in this study. FFR was measured in all patients for the evaluation of stenosis severity. Then TLR was performed when FFR was < 0.75, and TLR was deferred when FFR was > or = 0.75. Patients in whom TLR was deferred were followed up clinically (25 +/- 11 months). In 98 patients (67%) who underwent stress myocardial scintigraphy before angiography, the results of the scintigraphy were compared with FFR results. TLR was performed in 34 lesions (22%). After TLR, the Canadian Cardiovascular Society class decreased significantly (from 1.5 +/- 0.7 to 1.1 +/- 0.5; P < 0.05). In 113 patients who did not undergo TLR, only 4 patients (3.5%) had cardiac events (re-PCI in 1 patient and a positive SPECT in 3 patients). Discordance between the results of scintigraphy and FFR was observed in 30 patients (30%), but the patients who had good values of FFR > or = 0.75 showed a nil event rate (0%). FFR might be useful for the determination of the indication of TLR.