Attention deficit hyperactivity disorder (ADHD) is a behavioral disorder characterized by a persistent pattern of inattention and/or hyperactivity or impulsivity in more than one social setting. Among the behaviors contributing to functional impairment are difficulty focusing (sitting still, listening, following directions), fidgeting, restlessness, persistent motion (running, climbing, jumping), persistent interrupting and talking, and other behaviors that interfere with social, occupational, or academic function. Children may have academic deficits and more reported behavior problems at school.

Typically, symptoms present before age 12. When diagnosed in adults, presenting symptoms include inattention, restlessness, and impulsivity but also involve emotional dysregulation (angry outbursts, low threshold of frustration) and executive dysfunction (trouble organizing and completing tasks, missing appointments or deadlines). Hoarding symptoms may be present in up to 25% of adults with ADHD.

The prevalence of ADHD is about 5% in pediatric and 2.5% in adult populations. In children, ADHD is twice as common in boys compared to girls; however, girls are more likely to present with predominantly inattentive symptoms. Smoking exposure during fetal development, low birth weight, and a first-degree relative with ADHD are associated with increased risk for developing ADHD.