Recent studies have identified an association between moderate aortic stenosis (AS) and outcome. We assessed whether Digital Imaging and Communications in Medicine (DICOM) structured reporting (SR), which captures and inserts echocardiographic measurements and text data directly into radiological reports, may lead to misclassifying patients with severe AS as moderate.Moderate or severe AS cases were filtered from an echocardiography data set based on aortic valve area (AVA) < 1.5 cm, indexed AVA (AVAi) ≤ 0.85 cm/m, mean pressure gradient ≥ 25 mm Hg, dimensionless severity index (DSI) ≤ 0.5, or peak velocity > 3 m/sec. Data validation was conducted by verification of each parameter. All echocardiographic parameters and definitions of AS were compared pre- and postvalidation by taking differences in measurements. Misclassification rates were assessed by determining the percentage of cases that changed AS severity classification and impact on outcomes. Patients were followed over 4.3 ± 1.5 years.2Of 2,595 validated echocardiograms with AS, up to 36% of the echocardiographic parameters for AS criteria had a >10% difference between DICOM-SR and manual validation, the highest with mean pressure gradient (36%) and the lowest with DSI (6.5%). The validation process changed the reported degree of AS in up to 20.6% of echocardiograms with resultant changes in AS severity and its association with mortality or heart failure-related hospitalizations. In contrast to multiple quantitative metrics in DICOM-SR after manual validation, clinicians' evaluation of AS severity was unable to distinguish composite outcomes over 3 years between moderate and severe AS. The risk of composite outcomes was significantly increased when severe AS was evidenced by at least 1 echocardiographic parameter of severe AS (hazard ratio = 1.24; 95% CI, 1.12-1.37; P < .001). The greatest hazard was based on DSI only (hazard ratio = 1.26; 95% CI, 1.10-1.44; P < .001), which was higher after manual validation compared to DICOM-SR. Averaging of repeated echo measures including invalid values contributed the most to erroneous data.Nonpeak data in DICOM-SR led to incorrect categorization of a high proportion of patients based on AS severity definitions. Standardization of data fields and curation to ensure that only peak values are imported from DICOM-SR data are essential.