The impairments in motor performance could be related to the foot structure in children with attention-deficit/hyperactivity disorder (ADHD) while considering the close relationship between foot structure and lower extremity alignment. This study aimed to investigate the foot structure and its relationships between disease severity, physical activity and psychiatric traits in children with ADHD. Children with ADHD (n = 50; mean age: 12.02 +/- 1.83 years) and typically developing peers (n = 30; mean age: 12.86 +/- 2.56 years) were included. The static footprint analysis was collected by using digital images. The ImageJ program was used to calculate Clarke's angle, Staheli arch index (SAI) and Chippaux-Smirak index (CSI). The Turgay DSM-IV disruptive behavior disorders rating scale (T-DSM-IV-S), physical activity questionnaire for older children (PQ-C), children's depression inventory and state-trait anxiety inventory for children were all used to assess symptoms of ADHD, physical activity, depression, stress and anxiety, respectively. Approximately 52-53% of children with ADHD had mild to severe flatfoot, while only 8-13% of typically developing peers had flatfoot based on SAI and CSI (P = 0.01). Significant correlation was found between Clarke's angle and PQ-C (r = 0.21, P = 0.04). Besides, T-DSM-IV-S was significantly correlated with SAI (r = 0.24, P = 0.01) and CSI (r = 0.25, P = 0.01) in children with ADHD. Children with ADHD had a significantly greater tendency of flatfoot compared to typically developing peers. Besides, the deterioration of the foot structure of children with ADHD was associated with disease severity.