Background: In-hospital and 30-day mortality, 3-month functional outcome were reported as associated with endovascular treatment (EVT) case volume per hospital, but one-year mortality was unknown. Furthermore, the hospital EVT volume threshold based on one-year mortality was not reported. We aimed to investigate whether there was a correlation between annual EVT case volume per hospital and one-year mortality and suggest volume threshold. Methods: Data from Korean national survey for assessing quality of acute stroke care were used. The survey was conducted since 2005 and the subject was patients with acute stroke who were admitted via emergency rooms within 7 days of onset at hospitals treating 10 or more stroke cases during the three (2013, 2014) or six (2016) month survey period. Ischemic stroke cases treated with EVT during the last available three assessments (2013, 2014, and 2016) were selected for the analysis. Results: A total of 1,746 ischemic stroke cases (age, 69.2 ± 12.4years; male, 56.6%) treated in 120 hospitals with EVT were analyzed. The median annual EVT case volume was 12.0 cases per hospital (interquartile range, 6.0-22.9) and the mortality at one-month, three-month, and one-year were 12.7%, 16.6%, and 23.3%, respectively. When divided into quartiles according to the annual EVT case volume, the lowest quartile group was found to have the highest one-year mortality (odds ratio [95% confidence intervals], 1.49 [1.04-2.13]), adjusted for age, sex, NIHSS, onset to arrival time. Restricted cubic splines performed on the annual EVT case volume per hospital revealed that cut-off value for the probability of one-year mortality was 15 cases per year ( p <0.02) (Figure). Conclusions: There was an association between annual EVT case volume and one-year mortality, and the volume threshold per hospital based on the one-year mortality was found to be 15 EVT cases per year.