Background <p>The prevalence of mental disorders has been steadily rising due to aging populations, rapid urbanization, and social structural changes, posing significant public health challenges globally. Despite advances in pharmacological treatments, limited social functionality, high relapse risk, and adaptation difficulties persist in patients with mental disorders, emphasizing the critical need for rehabilitation services.</p> Methods <p>This study utilizes data from the Global Burden of Disease Study 2021 to analyze the burden of mental disorders and rehabilitation needs across 204 countries and territories. Age-standardized rates (ASR) and Years Lived with Disability (YLDs) were calculated, along with the Estimated Annual Percentage Change (EAPC). Patterns were examined for major mental disorders including developmental intellectual disability, schizophrenia, and autism spectrum disorders. Correlations with the Socio-Demographic Index (SDI) were assessed using Spearman analysis.</p> Findings <p>Between 1990 and 2021, the global prevalence of mental disorders decreased slightly in ASR (-0.19% EAPC), while the absolute number of cases increased by 34.8%. Rehabilitation needs for elderly women and young men surged significantly, particularly in low- and middle-income countries. SDI exhibited distinct associations with rehabilitation burdens, reflecting disparities in resource availability and regional improvements. Developmental intellectual disability displayed strong negative correlations with SDI, while schizophrenia and autism spectrum disorders showed positive correlations.</p> Interpretation <p>Findings highlight the urgency of prioritizing mental health resource allocation in vulnerable populations and high-burden regions. Integrated approaches incorporating Universal Health Coverage (UHC), SDI-based strategies, and international collaborations are essential to advancing equity in mental health rehabilitation globally.</p>