BACKGROUND: Thyroid cancer (TC) is the most common malignancy of the endocrine system and head-and-neck region, yet data on its burden in adolescents and young adults (AYAs) is lacking. This study aimed to estimate the global burden of TC among AYAs from 1990 to 2021. METHODS: Utilizing the Global Burden of Disease (GBD) 2021 data, we analyzed age-standardized rates of incidence, prevalence, and disability-adjusted life-years (DALYs) on global, regional, and national scales. Joinpoint regression was employed to determine average annual percentage change (AAPC), with frontier analysis revealing regions for improvement. Decomposition analysis assessed the impacts of population aging, growth, and epidemiological changes. Projections for disease burden extending to 2040 were generated using the Bayesian Age-Period-Cohort model. RESULT: In 2021, there were 48.2 thousand incident cases, 436.1 thousand prevalent cases, and 183.5 thousand DALYs worldwide. Meantime, the age-standardized incidence rates (ASIR), age-standardized prevalence rates (ASPR), and age-standardized DALYs rates (ASDR) were 1.6, 14.3 and 6.1 per 100 000, respectively. From 1990 to 2021, the ASIR, ASPR and ASDR increased with AAPCs of 1.73, 1.77, and 0.38, respectively. Socio-demographic resources in Saudi Arabia, Taiwan (Province of China), Iceland, United Arab Emirates, and United States Virgin Islands have the potential to lower ASDR due to TC among AYAs. Furthermore, 13.3 thousand and 34.9 thousand new cases occurred in the males and females in 2021. Among 5 age groups, the highest numbers of incidence, prevalence, and DALYs, along with ASRs, were observed in the 35-39 age group. Global projections indicated a continuous rise in numbers of incidence, prevalence, and DALYs, with estimates of 60.2 thousand, 558.4 thousand, and 199.7 thousand by 2040, respectively. CONCLUSION: The global burden of TC among AYAs was on the rise, with significant disparities by regions, genders, and age groups, highlighting the necessity for targeted and effective interventions.