Attention-deficit/hyperactivity disorder (ADHD) is a risk factor for substance abuse in adults. Additional psychiatric comorbidity increases this risk. ADHD is associated with different characteristics of substance abuse: substance abuse transitions more rapidly to dependence, and lasts longer in adults with ADHD than those without ADHD. Self-medication may be a factor in the high rate of substance abuse in adults with ADHD. While previous concerns arose whether stimulant therapy would increase the ultimate risk for substance abuse, recent studies have indicated that pharmacologic treatment appears to reduce the risk of substance abuse in individuals with ADHD. When treating adults with ADHD and substance abuse, clinicians should assess the relative severity of the substance abuse, the symptoms of ADHD, and any other comorbid disorders. Generally, stabilizing or addressing the substance abuse should be the first priority when treating an adult with substance abuse and ADHD. Treatment for adults with ADHD and substance abuse should include a combination of addiction treatment/psychotherapy and pharmacotherapy. The clinician should begin pharmacotherapy with medications that have little likelihood of diversion or low liability, such as bupropion and atomoxetine, and, if necessary, progress to the stimulants. Careful monitoring of patients during treatment is necessary to ensure compliance with the treatment plan.