Introduction <p>Few published population-based studies report the incidence or prevalence of juvenile myasthenia gravis (JMG) due to the rarity of the disorder. Despite recent progress in new targeted treatments and ongoing developments, there remains a critical need for novel and effective therapies specifically for JMG. Most treatments used for JMG are only approved for adult patients with MG. Thus, a thorough evaluation and understanding of the basic epidemiology of JMG is needed.</p> Methods <p>We conducted a population-based retrospective study to estimate the annual incidence and prevalence of JMG in the US from 2010 to 2020 by analyzing the Merative™ MarketScan^® Commercial Claims and Encounters Database (CCAE) and Multi-State Medicaid Database (MDCD).</p> Results <p>The incidence of JMG in 2020 was 5.9 [95% confidence interval (CI) 3.3–9.7] per million person-years in CCAE and 8.7 (95% CI 6.0–12.3) per million person-years in MDCD, with considerable variation across the study period. The prevalence of diagnosed JMG remained fairly consistent, with 25.3 (95% CI 19.9–32.2) per million population in CCAE and 37.6 (95% CI 31.9–44.4) per million population in MDCD in 2020. Both databases consistently showed higher incidence and prevalence among girls compared with boys. No clear pattern was observed in incidence by age of onset over the study period, whereas prevalence generally increased with age. Both incidence and prevalence by age of onset were higher in MDCD than CCAE. Furthermore, higher incidence and prevalence were observed among Black population compared with White population. Overall, no obvious increasing or decreasing trend was observed during the study period.</p> Conclusion <p>The incidence and prevalence of JMG in the US, previously understudied, may be higher than earlier research suggested, possibly due to limited research into the epidemiology of JMG. This finding implies that the actual burden of JMG could be greater than previously estimated.</p>