<p>The relationship between body mass index (BMI) and the risk of asthma in the pediatric population is not fully understood. This study aimed to investigate the association between BMI and asthma in a large nationally representative sample. The study included 35,603 pediatric participants from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020. The association between BMI and asthma was examined using various statistical models, including logistic regression, piece-wise linear regression, and subgroup analyses, adjusting for potential confounding factors. When analyzing BMI as a continuous variable, a one-unit increase in BMI was associated with a 4% higher odds of asthma. A clear dose-response relationship was observed, where individuals in the higher BMI quartiles had progressively higher odds of asthma compared to those in the lowest quartile. Smooth curve fitting revealed a not entirely linear relationship, with a steeper increase in asthma risk at lower BMIs (below an inflection point of 21&#xa0;kg/m²) compared to higher BMIs. Subgroup analyses consistently showed a positive association between BMI and asthma across different age, gender, race, socioeconomic, and smoking-related factors. Sensitivity analyses, including multiple imputation for missing data and alternative BMI metrics, confirmed the stability of the results. This study provides robust evidence for a positive and not entirely linear association between BMI and the risk of asthma in the pediatric population. These findings enhance the existing literature and underscore the necessity of considering BMI in both asthma research and clinical practice.</p>