To assess the agreement of clinical site and angiographic core laboratory readings obtained in the New Approaches to Coronary Intervention (NACI) registry, we reviewed the angiographic results obtained in 787 lesions assessed both by the sites and the core laboratory, including 135 lesions analyzed twice (> or =2 months apart) by the angiographic core laboratory. Although moderate agreement was demonstrated between the clinical site and angiographic core laboratory for qualitative lesion morphology such as lesion calcium (kappa [kappa] = 0.42), only fair agreement was found between site and core laboratory estimation of lesion ulceration (kappa = 0.33); thrombus (kappa = 0.30); and eccentricity (kappa = 0.27); with poor agreement for angulation (kappa = 0.16); and proximal vessel tortuosity (kappa = 0.03). Agreement for qualitative morphology was better for repeated core laboratory readings of lesion eccentricity (kappa = 0.75); angulation (kappa = 0.72); thrombus (kappa = 0.68); proximal vessel tortuosity (kappa = 0.66); and calcification (kappa = 0.64). Quantitative angiographic measurements correlated moderately between the clinical site using the digital caliper method and the core laboratory using the automated edge-detection method, including preprocedural percentage diameter stenosis (intraclass correlation [R] = 0.50) and postprocedural percentage diameter stenosis (R = 0.63). Repeated core laboratory readings had almost perfect agreement, with R ranging from 0.88 for postprocedural percentage diameter stenosis to 0.93 for reference vessel diameter and pre- and postprocedural minimal lumen diameters. Repeated angiographic core laboratory readings provided highly consistent quantitative and qualitative morphologic results in the NACI registry, but the core laboratory readings varied substantially from those obtained at the clinical site. More standardized angiographic analytic criteria and core laboratory feedback to investigators may improve agreement between the clinical sites and the angiographic core laboratory in subsequent studies.