This chapter discusses the relationship between attention-deficit/hyperactivity disorder (ADHD) and trauma in adolescents. Trauma is conceptualized as a frightening, violent, or dangerous event that poses a threat to an individual’s bodily integrity or life. Exposure to traumatic events can impact adolescent development, contributing to emotional distress and difficulties with regulation; adolescents who have been exposed to trauma may exhibit symptoms that are classically seen in youth with ADHD. It is important, therefore, to arrive at an accurate diagnostic impression of adolescents who are presenting with inattention and regulation difficulties. Clinicians are advised to evaluate for the potential contribution of trauma when diagnosing ADHD in adolescents. Arriving at a clear diagnostic understanding of an adolescent’s presenting concerns has significant implications for the treatment of these youth. Adolescents with trauma histories who present with symptoms of ADHD require multifaceted interventions that target their emotional functioning as well as behavioral presentation.