This study will take place in 'Children and adolescence health and sports center' in Meir Medical Center, Kfar-Saba, Israel. Forty-five children, boys and girls between the ages 6 and 18, with newly diagnosed ADHD that not receiving any drugs will be assigned to the intervention group. Age and gender matched children with ADHD, receiving Ritalin and not engaged in regular exercise, or healthy children's without ADHD will serve as controls. The intervention group will participate in an exercise program, including aerobic and anaerobic components, twice a week, for 3 months. Exercise testing, blood sampling and cognitive assessment will be performed at the start and in the end of this study.