Background Attention‐deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood and can be associated with obesity. The aim of this study was to reveal the connection between ADHD symptoms, food habits and obesity. Methods We examined 12 350 children (6010 boys, 6340 girls) from 27 elementary schools in Cheonan, the Republic of Korea. The study subjects were 5‐ to 13‐year‐old children (9.4 ± 1.7 years). Parents completed the DuPaul ADHD Rating Scale. Food habits were measured by a questionnaire adapted from the Korea Youth Risk Behavior Web‐based Survey and a validated mini‐dietary assessment tool. The full set of hypothesized associations was tested using covariance structural modelling. Results The prevalence of ADHD was 7.6% and that of obesity was 4.5% in our study population. The data was well fit by the model. ADHD was associated with body mass index (BMI; standardized β = 0.086, P < 0.001). Bulimic dietary behaviours was related to BMI (standardized β = 0.548, P < 0.001). Socio‐economic status was associated with BMI (standardized β = −0.017, P = 0.027). Conclusion Our analysis suggested that ADHD was a risk factor for obesity through dietary behavioural change and socio‐economic status.