Attention deficit hyperactivity disorder (ADHD) is a common childhood disorder that frequently persists into adulthood, with significant levels of inattentive, hyperactive and impulsive behavior. Impairments associated with adult ADHD include distress from the symptoms, impaired ability to function in work and academic settings, and problems sustaining stable relationships. The disorder is commonly associated with volatile moods, antisocial behavior, and drug and alcohol misuse. There is an increased risk of developing comorbid anxiety, depression, personality disorders, and drug and alcohol dependence. Despite the proven effectiveness of drugs such as methylphenidate, dexamphetamine and atomoxetine, few cases of ADHD are recognized and treated in the UK. The reasons for this are unclear, since most psychiatrists working with children and adolescents are aware that ADHD commonly persists into adult life and they also see the disorder affecting parents of children with ADHD. Issues of transition from the care of child to adult psychiatry and the need to refer adult relatives of children with ADHD to suitable psychiatric services are a major concern. Furthermore, many cases of adult ADHD go unrecognized or are seen by mental health teams that are not familiar with the subtleties of the adult presentation. As a result, misdiagnosis and treatment for conditions such as atypical depression, mixed affective disorder, cyclothymia, and borderline and unstable emotional personality disorders is not uncommon. There is therefore a requirement for further training in this area. This review will describe the common clinical presentation and provide guidelines for the diagnosis and treatment of ADHD in adults. Any psychiatrically trained physician using standard psychiatric assessment procedures can perform clinical evaluations for adult ADHD. As with other psychiatric disorders in adulthood, ADHD has its own characteristic onset, course and psychopathology. Symptoms of ADHD are trait-like, being stable characteristics from early childhood, and commonly co-occur with affective instability. Stimulants are the mainstay of treatment and are effective in around 70% of cases. Psychotherapeutic interventions also have an important role. These guidelines will assist psychiatrists and other adult mental health workers in identifying and treating individuals with adult ADHD.