BACKGROUND In the United States, efforts are underway to improve timely access to percutaneous coronary intervention in ST-elevation myocardial infarction (STEMI). The Joint Commission (TJC) and the American College of Cardiology National Cardiovascular Data Registry (NCDR) have developed standardized definitions and clinical performance measures for STEMI. The purpose of this study was to determine differences in 3 quality-assurance registries for STEMI patients. METHODS AND RESULTS STEMI patients presenting to the Minneapolis Heart Institute at Abbott Northwestern Hospital (Minneapolis, Minn) are tracked by 3 distinct quality assurance programs: NCDR, TJC, and the level 1 MI registry (a regional system for percutaneous coronary intervention in STEMI which includes transfer patients). Over 1 year, we examined consecutive STEMI patients in level 1 and compared them with individuals meeting NCDR and TJC inclusion criteria. Of 501 STEMI patients treated using the level 1 MI protocol, 422 patients had a clear culprit (402 percutaneous coronary intervention, 13 coronary artery bypass grafting, 7 medical management). In the same period, 282 patients met inclusion criteria for NCDR (56% of the level 1 population), and 66 met inclusion criteria for TJC (13% of the level 1 population). Transfer patients (n=380) accounted for 87% of the discrepancy between level 1 and TJC. Pharmacoinvasive percutaneous coronary intervention (n=102) accounted for 47% of the discrepancy between level 1 and NCDR. CONCLUSIONS Current inclusion criteria for enrollment in STEMI registries are not uniform. This may lead to variable quality assurance outcomes for the same patient cohort and has important implications for standardized quality measurement.