Objectives: The main objective of this study is to determine the correlation between fractional flow reserve (FFR)- and frequency domain optical coherence tomography (FD-OCT)-measured lumen parameters, and to determine the diagnostic competence of FD-OCT concerning the identification of severe coronary stenosis.Methods: A total of 41 coronary stenoses in 30 patients were assessed consecutively by quantitative coronary angiography (QCA), FFR, and FD-OCT. Stenoses were labeled severe if FFR <= 0.80. The minimal lumen area (MLA), minimal lumen diameter (MLD), and percent lumen area stenosis (%AS) were measured using FD-OCT.Results: FFR was <= 0.80 in 10 stenoses (24.4%). A poor but significant correlation between FFR and FD-OCT-measured MLA (r(2)=0.4, p<0.001), MLD (r(2)=0.28, p < 0.001), and %AS (r(2)=0.13, p=0.02) was found. In the overall group, the diagnostic efficiency of MLA and MLD in identifying significant stenosis was moderate. The area under the curve (AUC) was 0.80 [95% confidence interval (Cl): 0.64-0.91] for MLA and 0.76 (95% CI: 0.60-0.88) for MLD. The best cut-off values of FD-OCT-measured lumen parameters to identify stenosis with FFR <= 0.80 were 1.62 mm(2) [specificity 97%, sensitivity 70%, positive predictive value (PPV) 89% and negative predictive value (NPV) 91%] for MLA and 1.23 mm (specificity 87%, sensitivity 70%, PPV 64% and NPV 90%) for MLD. The diagnostic efficiency of MLA in identifying significant stenosis in vessels having reference diameter < 3 mm was high. The AUC was 0.96 (95% CI: 0.83-1.0).Conclusions: The FFR values and FD-OCT anatomical parameters MLA, MLD were found to be significantly correlated. In the overall group, the FD-OCT-measured MLA and MLD have shown moderate diagnostic efficiency in the functional evaluation of significant stenosis. FD-OCT-measured MLA has high diagnostic efficiency in identifying severe coronary stenosis in vessels having reference diameter <3 mm. (C) 2013 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.