BACKGROUND - Fractional flow reserve predicts cardiac events after coronary stent implantation. The aim of the present study was to assess the 9-month angiographic in-stent restenosis rate in the setting of optimal stenting and a persisting gradient distal to the stent as assessed by a pressure wire pullback recording in the entire length of the artery. METHODS AND RESULTS - In 98 patients with angina pectoris, 1 de novo coronary lesion was treated with a bare-metal stent. After stent implantation, pressure wire measurements (Pd=mean hyperemic coronary pressure and Pa=mean aortic pressure) were performed in the target vessel: (1) Pd/Pa as distal to the artery as possible (fractional flow reserve per definition); (2) Pd/Pa just distal to the stent; (3) Pd/Pa just proximal to the stent; and (4) Pd/Pa at the ostium. Residual abnormal Pd/Pa was defined as a pressure drop between Pd/Pa measured at points 1 and 2. Fractional flow reserve distal to the artery after stenting was significantly lower (0.88±0.21 versus 0.97±0.05; P<0.001), and angiographic in-stent binary restenosis rate was significantly higher (44.0% versus 8.1%; P<0.001) in vessels with a residual abnormal Pd/Pa. Residual abnormal Pd/Pa (odds ratio, 4.39; 95% confidence interval, 1.10 to 18.16; P=0.034), reference vessel size (odds ratio, 0.17; 95% confidence interval, 0.04 to 0.69; P=0.013), and stent length (odds ratio, 1.11; 95% confidence interval, 1.03 to 1.21; P=0.009) were predictors of angiographic in-stent restenosis after 9 months. CONCLUSIONS - A residual abnormal Pd/Pa distal to a bare-metal stent was an independent predictor of in-stent restenosis after implantation of a coronary bare-metal stent.