The National Institute of Drug Abuse is supporting this project, which will identify structural and functional characteristics of the brain that distinguish young adults with Attention Deficit Hyperactivity Disorder (ADHD) from similar young adults without a history of ADHD. The project is an extension of the long-standing Multimodal Treatment Study of ADHD (MTA), a 14-year longitudinal study of participants followed at multiple sites in North America. A subset of MTA participants, both with and without childhood ADHD, will be studied with a multimodality brain imaging examination, as well as with other neurobehavioral assessments, as part of this recently funded MTA neuroimaging study. Many aspects of the brain’s architecture will be examined, including the structure of the fiber tracts that connect brain regions, as will brain responses to task demands and the pattern of functional interactions within the brain. The focus of the study will be on correlates of drug and alcohol use in the study participants, as well as effects that might be linked to long-term use of stimulant medications.