Attention-deficit/hyperactivity disorder (ADHD) is a chronic, lifelong neurobeha-vioral disorder with childhood-onset, which seriously impairs the affected adults in a variety of daily living functions like academic, social and occupational functioning. Prevalence of ADHD declines with age in the general population. The approximate prevalence rates of ADHD is 8% in childhood, 6% in adolescence and 4% in adulthood. The unclear validity of DSM-IV diagnostic criteria for this condition can lead to reduced prevalence rates by underestimation of the prevalence of adult ADHD. The disorder is characterized by behavioral symptoms of inattention, hyperactivity, and impulsivity across the life cycle and is associated with considerable morbidity and disability. Although its etiology remains unclear, considerable evidence documents its strong neurobiological and genetic underpinnings. ADHD is associated with a high percentage of comorbid psychiatric disorders in every lifespan. In adulthood between 65-89% of all patients with ADHD suffer from one or more additional psychiatric disorders, above all mood and anxiety disorders, substance use disorders and personality disorders, which complicate the clinical picture in terms of diagnostics, treatment and outcome issues. The high comorbidity with other psychiatric disorders, the resulting deficits in social competences and risky health behavior that often go along with a diminished life quality must be stressed in these patients. Preventive and therapeutic interventions should be taken at an early stage to counteract the possible negative influences of ADHD on functioning and relationships. In this paper, we reviewed the historical aspects, epidemiology, neurobiology, comorbidity, diagnostic difficulties and clinical features of adult ADHD
