Advances in imaging technology allow unprecedented access to the anatomy and physiology of the living, growing human brain. Anatomical imaging studies of individuals with attention deficit/hyperactivity disorder (ADHD) consistently point to involvement of the frontal lobes, basal ganglia, corpus callosum, and cerebellum. Imaging studies of brain physiology also support involvement of right frontal-basal ganglia circuitry with a powerful modulatory influence from the cerebellum. Although not currently of diagnostic utility, further extension and refinement of these findings may offer hope for greater understanding of the core nature of ADHD and possible subtyping to inform treatment interventions.