Objective: The objective of this study is to explore the effects of a moderate- to high-intensity physical activity program on fitness, cognitive functions, and ADHD-related behavior in children with ADHD. Method: Fitness level, motor skills, behaviors, and cognitive functions are assessed by standardized tests before and after a 10-week training or control period. Results: Findings show that participation in a physical activity program improves muscular capacities, motor skills, behavior reports by parents and teachers, and level of information processing. Conclusion: A structured physical activity program may have clinical relevance in the functional adaptation of children with ADHD. This supports the need for further research in the area of physical activity with this population. (Contains 1 figure and 3 tables.)