BACKGROUND: This study aimed to estimate the disease burden of ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and overall stroke among young adults (aged 15-49 years) in 204 countries and territories from 1990 to 2021, along with the associated risk factors. METHODS: GBD (Global Burden of Disease Study) 2021 data were used to assess the burden and trends via age-standardized rates and their estimated annual percentage changes. RESULTS: Although age-standardized rates generally declined from 1990 to 2021, the number of incident and prevalent stroke cases among young adults increased by 36% (95% uncertainty interval, 31%-41%) and 41% (95% uncertainty interval, 38%-43%), respectively. Notably, from 2015 to 2021, the age-standardized incidence of ischemic stroke and subarachnoid hemorrhage among young adults increased, with estimated annual percentage changes of 0.65 (95% CI, 0.39-0.92) and 0.58 (95% CI, 0.47-0.69), respectively. High systolic blood pressure was the primary risk factor for stroke-related disability-adjusted life-years among young adults. However, other risk factors varied by region, with higher proportions of smoking, high low-density lipoprotein cholesterol, and high body mass index in high sociodemographic index regions, and higher proportions of household air pollution from solid fuels and diet low in vegetable in low sociodemographic index regions. From 1990 to 2021, the total number of stroke-related disability-adjusted life-years among young adults due to risk factors increased by 12% (95% uncertainty interval, 2%-22%), driven principally by high systolic blood pressure, ambient particulate matter pollution, high body mass index, high low-density lipoprotein cholesterol, and high fasting blood glucose. CONCLUSIONS: Since 2015, there has been a concerning rebound in the age-standardized incidence rates of ischemic stroke and subarachnoid hemorrhage among young adults globally. Given regional and sociodemographic index variations in risk factors, targeted and cost-effective policies and interventions are urgently needed to reduce stroke burden in this demographic.