BACKGROUND AND PURPOSE:In Orange County, California, patients with suspected acute stroke are taken to stroke neurology receiving centers that are designated by County Emergency Medical Services authorities as either hubs or spokes based on endovascular treatment capability. We examined relationships between stroke details, reperfusion therapies, hospital transfers, and their change over time. METHODS:All patients from January 1, 2013, to December 31, 2015, for whom 911 was called within 7 hours of onset in whom Emergency Medical Services personnel suspected acute stroke were evaluated. RESULTS:Among 6132 patients, 3924 (64%) had confirmed diagnosis of stroke (74% ischemic/26% hemorrhagic), yielding diagnostic precision of 64% in the field. Of the 2892 patients with acute ischemic stroke, acute reperfusion therapy was given to 29.2% (21.7% intravenous tPA [tissue-type plasminogen activator] only and 7.5% endovascular treatment). Rates of endovascular treatment of patients with ischemic stroke increased over time, more than doubling from 5.6% in 2013 to 12.5% (odds ratio per 3-month quarter=1.09; 95% confidence interval, 1.04-1.14; P<0.0001). Only 3.4% of patients with acute ischemic stroke were transferred from a spoke to a hub hospital; transfer rates were inversely related to age (P<0.0001), and reperfusion therapy rates did not vary according to transfer status. CONCLUSIONS:Favorable features of this acute stroke care system include reperfusion therapy in 29.2% of patients with ischemic stroke and substantial increases in endovascular treatment rates over time. Continued efforts to optimize acute stroke systems of care can be directed toward improving access to best acute stroke therapies.