Attention Deficit Hyperactivity Disorder (ADHD) is a common and impairing neuropsychiatric disorder of childhood, occurring in 3 to 5% of all school-age children. This disorder is associated with greater risks for low academic achievement, school dropouts, poor family and peer relations, aggression, substance abuse, driving accidents and chronic problems in adult adaptation. As such, it has an enormous impact on the utilization of medical and health care services, and the direct and indirect costs of this disorder are high. However, in a large number of children symptoms dissipate as they grow up and they go on to function normally and lead typical lives. This has lead to speculation that ADHD may not so much represent a disruption, as a delay of brain development. This aim of this study is to address this issue.

There is a growing body of research supporting the existence of deficits in brain anatomy associated with ADHD, with evidence of reductions in overall brain size, cortical gray matter and subcortical structures. However, reported effect sizes are small and results not always consistent. Anatomical MRI studies may be easily confounded, as brain development is complex and associated with both progressive and regressive changes in brain anatomy. In this study, we propose to combine longitudinal data from a large cohort of children and adolescents with state-of-the-art imaging methods (including diffusion tensor imaging and voxelbased morphometry) to investigate brain development in ADHD. This will allow us to address the question whether ADHD represents a disruption or a delay of brain development.