['The benefits of intravenous tissue-plasminogen activator (tPA) in acute ischemic stroke are time-dependent. Emergency medical services (EMS) hospital prenotification of an incoming patient with potential stroke may provide a means of reducing evaluation and treatment times and improving treatment rates; yet, available data are limited.', 'We examined 371 988 patients with acute ischemic stroke transported by EMS and enrolled in Get With The Guidelines-Stroke from April 1, 2003, to March 31, 2011. Prenotification occurred in 249 197 (67.0%) of EMS-transported patients. Among eligible patients arriving by 2 hours, patients with EMS prenotification were more likely to be treated with tPA within 3 hours (82.8% versus 79.2%, absolute difference +3.5%, P<0.0001, the National Institutes of Health Stroke Scale-documented cohort; 73.0% versus 64.0%, absolute difference +9.0%, P<0.0001, overall cohort). Patients with EMS prenotification had shorter door-to-imaging times (26 minutes versus 31 minutes, P<0.0001), shorter door-to-needle times (78 minutes versus 80 minutes, P<0.0001), and shorter symptom onset-to-needle times (141 minutes versus 145 minutes, P<0.0001). In multivariable and modified Poisson regression analyses accounting for the clustering of patients within hospitals, use of EMS prenotification was independently associated with greater likelihood of door-to-imaging times ≤25 minutes, door-to-needle times for tPA ≤60 minutes, onset-to-needle times ≤120 minutes, and tPA use within 3 hours.'] Is emergency medical service hospital prenotification associated with improved evaluation and treatment of acute ischemic stroke?