Reports published over the past decade indicate that attention deficit hyperactivity disorder (ADHD) is a cause of significant psychological impairment in adults. The adulthood disorder occurs as a continuation of its childhood counterpart, with the full ADHD syndrome persisting into early adulthood in about a third of those with childhood ADHD. Despite advances in the understanding of the neurobiology of adult ADHD, the diagnosis is made clinically by establishing a retrospective childhood diagnosis, evaluating the current symptom profile and excluding alternative medical or psychiatric causes of symptoms. Adults with ADHD have high rates of comorbid psychiatric disorder and suffer significant relationship dysfunction, work and educational failure. There is emerging evidence for the effectiveness of specific treatments for adult ADHD, including stimulant medications and some antidepressants. Clinicians should be aware of this potentially treatable disorder in young adults presenting with psychological difficulties and a history of childhood ADHD symptoms.