BACKGROUND Nationally endorsed, clinical performance measures are available that allow for quality reporting using electronic health records (EHRs). To our knowledge, how well they reflect actual quality of care has not been studied. We sought to evaluate the validity of performance measures for coronary artery disease (CAD) using an ambulatory EHR. METHODS We performed a retrospective electronic medical chart review comparing automated measurement with a 2-step process of automated measurement supplemented by review of free-text notes for apparent quality failures for all patients with CAD from a large internal medicine practice using a commercial EHR. The 7 performance measures included the following: antiplatelet drug, lipid-lowering drug, beta-blocker following myocardial infarction, blood pressure measurement, lipid measurement, low-density lipoprotein cholesterol control, and angiotensin-converting enzyme inhibitor or angiotensin receptor blocker for patients with diabetes mellitus or left ventricular systolic dysfunction. RESULTS Performance varied from 81.6% for lipid measurement to 97.6% for blood pressure measurement based on automated measurement. A review of free-text notes for cases failing an automated measure revealed that misclassification was common and that 15% to 81% of apparent quality failures either satisfied the performance measure or met valid exclusion criteria. After including free-text data, the adherence rate ranged from 87.5% for lipid measurement and low-density lipoprotein cholesterol control to 99.2% for blood pressure measurement. CONCLUSIONS Profiling the quality of outpatient CAD care using data from an EHR has significant limitations. Changes in how data are routinely recorded in an EHR are needed to improve the accuracy of this type of quality measurement. Validity testing in different settings is required.