Key Points: Question: What is the median door-in-door-out time for interhospital transfer of patients with stroke, and what patient and hospital-level factors are associated with door-in-door-out time? Findings: In this retrospective US registry–based study that included 108 913 patients with acute stroke requiring interhospital transfer from 1925 hospitals, the median door-in-door-out time was 174 minutes. Age 80 years or older, female sex, Black race, and Hispanic ethnicity were significantly associated with longer door-in-door-out times, whereas emergency medical services prenotification, severe stroke, and ischemic stroke eligible for endovascular therapy were significantly associated with shorter times. Meaning: This US registry–based study evaluated door-in-door-out times for patients with acute stroke requiring interhospital transfer and identified disparities and health system factors that could be possible targets for quality improvement initiatives. Importance: Treatments for time-sensitive acute stroke are not available at every hospital, often requiring interhospital transfer. Current guidelines recommend hospitals achieve a door-in-door-out time of no more than 120 minutes at the transferring emergency department (ED). Objective: To evaluate door-in-door-out times for acute stroke transfers in the American Heart Association Get With The Guidelines-Stroke registry and to identify patient and hospital factors associated with door-in-door-out times. Design, Setting, and Participants: US registry–based, retrospective study of patients with ischemic or hemorrhagic stroke from January 2019 through December 2021 who were transferred from the ED at registry-affiliated hospitals to other acute care hospitals. Exposure: Patient- and hospital-level characteristics. Main Outcomes and Measures: The primary outcome was the door-in-door-out time (time of transfer out minus time of arrival to the transferring ED) as a continuous variable and a categorical variable (≤120 minutes, >120 minutes). Generalized estimating equation (GEE) regression models were used to identify patient and hospital-level characteristics associated with door-in-door-out time overall and in subgroups of patients with hemorrhagic stroke, acute ischemic stroke eligible for endovascular therapy, and acute ischemic stroke transferred for reasons other than endovascular therapy. Results: Among 108 913 patients (mean [SD] age, 66.7 [15.2] years; 71.7% non-Hispanic White; 50.6% male) transferred from 1925 hospitals, 67 235 had acute ischemic stroke and 41 678 had hemorrhagic stroke. Overall, the median door-in-door-out time was 174 minutes (IQR, 116-276 minutes): 29 741 patients (27.3%) had a door-in-door-out time of 120 minutes or less. The factors significantly associated with longer median times were age 80 years or older (vs 18-59 years; 14.9 minutes, 95% CI, 12.3 to 17.5 minutes), female sex (5.2 minutes; 95% CI, 3.6 to 6.9 minutes), non-Hispanic Black vs non-Hispanic White (8.2 minutes, 95% CI, 5.7 to 10.8 minutes), and Hispanic ethnicity vs non-Hispanic White (5.4 minutes, 95% CI, 1.8 to 9.0 minutes). The following were significantly associated with shorter median door-in-door-out time: emergency medical services prenotification (−20.1 minutes; 95% CI, −22.1 to −18.1 minutes), National Institutes of Health Stroke Scale (NIHSS) score exceeding 12 vs a score of 0 to 1 (−66.7 minutes; 95% CI, −68.7 to −64.7 minutes), and patients with acute ischemic stroke eligible for endovascular therapy vs the hemorrhagic stroke subgroup (−16.8 minutes; 95% CI, −21.0 to −12.7 minutes). Among patients with acute ischemic stroke eligible for endovascular therapy, female sex, Black race, and Hispanic ethnicity were associated with a significantly higher door-in-door-out time, whereas emergency medical services prenotification, intravenous thrombolysis, and a higher NIHSS score were associated with significantly lower door-in-door-out times. Conclusions and Relevance: In this US registry–based study of interhospital transfer for acute stroke, the median door-in-door-out time was 174 minutes, which is longer than current recommendations for acute stroke transfer. Disparities and modifiable health system factors associated with longer door-in-door-out times are suitable targets for quality improvement initiatives. This retrospective study involving patients with acute stroke requiring transfers from hospitals in the Get With the Guidelines–Stroke registry assesses patient and hospital factors associated with door-in-door-out times. [ABSTRACT FROM AUTHOR]