Background <p>Nasopharynx cancer (NPC) is a highly aggressive malignancy that is relatively rare on a global scale but exhibits marked geographic clustering, with high incidence in regions such as Southeast Asia, North Africa, and the Middle East. However, comprehensive global epidemiological assessments remain limited. This study analyzed temporal trends in the prevalence of NPC among adolescents and young adults (AYAs) from 1990 to 2021 using an age-period-cohort (APC) model.</p> Methods <p>This study utilized data from the Global Burden of Disease 2021. The study population comprised individuals aged 15–39 years. Age-standardized prevalence rates (ASPR) were calculated, with net and local drift used to assess overall and age-specific trends. The APC model was employed to separate the independent effects of age, period, and birth cohort on changes in NPC prevalence.</p> Results <p>From 1990 to 2021, the number of NPC cases among AYAs globally increased by 89.16%, reaching 128278.84 cases in 2021, although the ASPR rose only slightly (+0.21%/year, 95% CI: −0.02 to 0.44). A marked increase in ASPR was observed in the high-middle SDI region (+1.70%/year, 95% CI: 1.30 to 2.11), contrasting with declining trends in high SDI and low SDI regions. The age effect demonstrated increasing NPC prevalence with age, peaking in the 35–39 age group. Period effects revealed a resurgence in NPC risk after globally 2010, particularly in rapidly industrializing high-middle SDI regions. Birth cohort effects improved in high SDI regions but did not show significant improvement in high-middle SDI regions.</p> Conclusion <p>NPC among AYAs shows divergent regional trends, with sharp increases observed in high-middle SDI regions, suggesting a need for further investigation into region-specific risk patterns and public health responses to address the growing burden, particularly in resource-limited settings.</p>