BACKGROUND: Hospital mortality is an important quality measure for acute myocardial infarction care. There is a concern that despite risk adjustment, percutaneous coronary intervention hospitals accepting a greater volume of high-risk ST elevation myocardial infarction (STEMI) transfer patients may have their reported mortality rates adversely affected. METHODS: The STEMI patients in the National Cardiovascular Data RegistryAcute Coronary Treatment Intervention Outcomes Network Registry-Get With the Guidelines from April 2011 to December 2013 were included. High-risk STEMI was defined as having either cardiogenic shock or cardiac arrest on first medical contact. Receiving hospitals were divided into tertiles based on the ratio of high-risk STEMI transfer patients to the total number of STEMI patients treated at each hospital. Using the Action Coronary Treatment Intervention Outcomes Network Registry-Get With the Guidelines in-hospital mortality risk model, we calculated the difference in risk-standardized in-hospital mortality before and after excluding high-risk STEMI transfers in each tertile. RESULTS: Among 119,680 STEMI patients treated at 539 receiving hospitals, 37,028 (31%) were transfer patients, of whom 4,500 (12%) were highrisk. The proportion of high-risk STEMI transfer patients ranged from 0% to 12% across hospitals. Unadjusted mortality rates in the low-, middle-, and high-tertile hospitals were 6.0%, 6.0%, and 5.9% among all STEMI patients and 6.0%, 5.5%, and 4.6% after excluding high-risk STEMI transfers. However, risk-standardized hospital mortality rates were not significantly changed after excluding high-risk STEMI transfer patients in any of the 3 hospital tertiles (low, -0.04%; middle, -0.05%; and high, 0.03%). CONCLUSIONS: Risk-adjusted in-hospital mortality rates were not adversely affected in STEMI-receiving hospitals who accepted more high-risk STEMI transfer patients when a clinical mortality risk model was used for risk adjustment.