BACKGROUND: There is limited information on the delivery of acute stroke therapies and secondary preventive measures and clinical outcomes over time in young adults with acute ischemic stroke. This study investigated whether advances in these treatments improved outcomes in this population. METHODS: Using a prospective multicenter stroke registry in Korea, young adults (aged 18–50 years) with acute ischemic stroke hospitalized between 2008 and 2019 were identified. The observation period was divided into 4 epochs: 2008 to 2010, 2011 to 2013, 2014 to 2016, and 2017 to 2019. Secular trends for patient characteristics, treatments, and outcomes were analyzed. RESULTS: A total of 7050 eligible patients (mean age, 43.1; men, 71.9%) were registered. The mean age decreased from 43.6 to 42.9 years ( P _trend =0.01). Current smoking decreased, whereas obesity increased. Other risk factors remained unchanged. Intravenous thrombolysis and mechanical thrombectomy rates increased over time from 2008 to 2010 to 2017 to 2019 (9.5%–13.8% and 3.2%–9.2%, respectively; P _trend <0.01). Door-to-needle time improved ( P _trend <.001), but onset-to-door and door-to-puncture times remained constant. Secondary prevention, including dual antiplatelets for noncardioembolic minor stroke (26.7%–47.0%), direct oral anticoagulants for atrial fibrillation (0.0%–56.2%), and statins for large artery atherosclerosis (76.1%–95.3%) increased ( P _trend <0.01). Outcome data were available from 2011. One-year mortality (2.5% in 2011–2013 and 2.3% in 2017–2019) and 3-month modified Rankin Scale scores 0 to 1 (68.3%–69.1%) and 0 to 2 (87.6%–86.2%) remained unchanged. The 1-year stroke recurrence rate increased (4.1%–5.5%; P _trend =0.04), although the difference was not significant after adjusting for sex and age. CONCLUSIONS: Improvements in the delivery of acute stroke treatments did not necessarily lead to better outcomes in young adults with acute ischemic stroke over the past decade, indicating a need for further progress.