Background: Acute ischemic stroke (AIS) patients are frequently transferred between hospitals, however it is not clear whether these transfers are optimized with respect to proximity and quality of the destination hospital. Our primary object was to identify hospital characteristics associated with sending and receiving AIS patients. Methods: Using a comprehensive statewide dataset, we identified all AIS patient transfers occurring between all 78 Massachusetts (MA) hospitals from 2007 and 2015. Hospital variables included hospital quality reputation (US News & World Report), hospital capabilities (stroke center status, annual stroke volume, and trauma center designation), and institutional affiliations (same vs. not). We also included network variables to control for the structure of hospital-to-hospital transfers. We used relational event modeling to account for complex temporal and relational dependencies associated with patient transfers. This method decomposes events into a decision to transfer, and if so, the receiving hospital destination, and models them using a discrete-choice framework. Results: Among 73,114 AIS admissions in MA during the 8-year study period, there were 7,189 (9.8%) transfers. After accounting for travel time between hospitals and structural network characteristics, factors associated with increased likelihood of being a receiving hospital included teaching hospital status, hospitals of the same or higher quality, the same or higher stroke center status, and the same hospital affiliation (Table). Conclusion: Patients experiencing AIS in MA are frequently transferred between hospitals. After accounting for multiple relevant hospital characteristics, hospital affiliation remains an important factor in determining transfer destination. While there may be some benefits to hospital affiliation, stroke systems of care should be designed to maximize patient benefit and leverage interfacility transfer accordingly.