INTRODUCTION: The purpose of this article is to describe the global burden and temporal trends of Alzheimer's disease and other dementias from 1990 to 2021 and explore cross-country inequality associated with sociodemographic development-related factors. METHODS: The disability-adjusted life years of Alzheimer's disease and other dementias and sociodemographic index were extracted from the Global Burden of Disease 2021 study, and other sociodemographic development-related factors, including government expenditure on education (% of GDP), net national income per capita, health expenditure per capita, and fertility rate, were sourced from World Bank Data. Disability-adjusted life years of Alzheimer's disease and other dementias across 204 countries/territories and global age-sex distribution in 2021 were illustrated. The Joinpoint regression model was used to analyze the temporal trends of disease burden, and the slope index of inequality and concentration index were calculated to quantify cross-country inequalities. Analyses were conducted in 2024. RESULTS: Significant disparities were observed in the numbers, rates, and age-standardized rates of disability-adjusted life years across 204 countries/territories. Females demonstrated higher disability-adjusted life year numbers (rates) for all age groups. Age-standardized disability-adjusted life year rate increased worldwide and was high in high-middle and middle sociodemographic index regions but increased faster in low (average annual percentage change=0.227%) and low-middle (average annual percentage change=0.244%) sociodemographic index regions. Cross-country inequality analyses indicated that disability-adjusted life years of Alzheimer's disease and other dementias were skewed and higher in countries with higher sociodemographic development, and the inequality increased with time except for education expenditure-related inequality. CONCLUSIONS: The burden of Alzheimer's disease and other dementias has risen globally over the past 3 decades, accompanied by increasing cross-country inequalities, which disproportionately affects countries with high sociodemographic development. Boosting expenditure on education may narrow this inequality.