The Mount Sinai School of Medicine is conducting a research study to evaluate the effects of Guanfacine (INTUNIV), a medication used in treatment of Attention Deficit Hyperactivity Disorder (ADHD) on brain activation. All participants receive, at no cost: a comprehensive physical exam, a comprehensive psychiatric interview, abbreviated psychological assessment, abbreviated cognitive testing, pre and post treatment fMRI scanning, weekly visits with our study physicians, referral back to primary clinician with progress report of participation, after being stabilized on the medication that works best for the child. Criteria for participation are: confirmed or suspected diagnosis of ADHD, ages 8-15 years, have no metal placed permanently in the body, able to enter and lie still in a scanner for about 1 hour while playing a videogame, and be healthy enough to participate in medication treatment with guanfacine. Contact Beth Krone at 212-659-8833, beth.krone@mssm.edu or P.I. Jeffrey Newcorn at Jeffrey.newcorn@mssm.edu. GCO 09-1825, IRB approved 11/3/11 to 11/2/12.