This report examines the developmental relationship between attention-deficit/hyperactivity disorder (ADHD) and substance use disorders (SUD) and associated concurrent disorders relative to adolescents and adults. ADHD is a risk factor for the development of SUD in adulthood, and it is particularly of concern with conduct and bipolar disorder comorbidities. Conversely, approximately one fifth of adults with SUD have ADHD. Individuals with SUD and ADHD have a more severe and complicated course of SUD. Pharmacotherapeutic treatment of ADHD in children reduces the risk for later cigarette smoking and SUD in adulthood.