Objective: To assess global and regional trends in infertility burden among reproductive-aged women with polycystic ovary syndrome (PCOS) from 1990 to 2021. Design: Longitudinal observational study. Setting: Global data from the Global Burden of Disease (GBD) 2021 database. Population: Women aged 15-49 years diagnosed with PCOS in 204 countries and territories. Methods: We extracted data on PCOS prevalence and associated infertility from the GBD 2021 dataset. Infertility was categorized into primary and secondary types. Analyses were conducted across age groups, GBD regions, and socio-demographic index (SDI) levels. Trends were quantified using estimated annual percentage change (EAPC), and associations between infertility burden and SDI were evaluated. Main outcome measures: Age- and region-specific prevalence of PCOS and the proportion of associated infertility, including subtype distribution and temporal change. Results: From 1990 to 2021, global PCOS cases increased from 34.8 to 65.8 million. Infertility among these women rose from 18.22% to 19.00%, with the highest proportion (21.9%) in the 35-39 age group. Low-SDI regions had fewer cases but higher infertility proportions. Equatorial Guinea showed the largest increase in infertility cases (+772%), while the Central African Republic had the highest proportion in 2021 (21.84%). An inverse correlation was observed between SDI and infertility proportion. Conclusions: The global burden of PCOS-related infertility has grown over the past three decades, with significant disparities by age, region, and development level. Targeted strategies are needed to improve reproductive care access and reduce inequities, particularly in low-SDI settings.