Our study aimed to quantitatively estimate the association of age at menarche with the risk of childhood- and adult-onset asthma separately.A retrospective cohort study of 24,282 US girls and women aged less than 80 years was conducted using continuous NHANES data from 2001-2018, and Cox proportional hazards regression models with censoring ages of 19 and 79 years were employed to separately estimate hazard ratios of childhood- and adult-onset asthma associated with age at menarche.Each one-year increase in age at menarche was significantly associated with a 16% (hazard ratio (HR) = 0.84; 95% confidence interval (CI): 0.77-0.91) decrease in the risk of childhood-onset asthma. Compared with age at menarche of 12-14 years, we observed a 56% (HR = 1.56; 95% CI: 1.19-2.04) increased risk of childhood-onset asthma for early menarche (age at menarche < 12 years) and a 40% (HR = 0.60; 95% CI: 0.32-1.10) decreased risk for late menarche (age at menarche ≥15 years). Race, family income, BMI, education and a family history of asthma did not modify these associations. No significant association was noted between age at menarche and adult-onset asthma.These results demonstrate that early menarche may represent a risk factor for childhood-onset asthma in the US, indicating the need for timely and effective management of individuals with early menarche to prevent asthma.Copyright © 2023. Published by Elsevier Inc.