A method of diagnosing attention deficient-hyperactivity disorder (ADHD) in a human patient by assessing the level of dopamine transporter in at least one region of the patient's central nervous system, where an elevated level of dopamine transporter in the patient is indicative of ADHD. In embodiments of the invention, assessment of dopamine transporter levels includes assessing binding of a dopamine transporter ligand to the dopamine transporters using PET or SPECT.