Attention-deficit/hyperactivity disorder (ADHD) is a common (5-10%) childhood-onset neuropsychiatric disorder worldwide among children and adolescents with 50- 60% persistence to adulthood (3-4%). Western studies have revealed a wide range of family/social/occupational impairment and neurocognitive deficits in adults with ADHD. However, there is limited data on the treatment effect for adults with ADHD worldwide and there is lack of information about adult ADHD in Taiwan. In view of this, it is warranted to conduct a study on the clinical, functional, and neurocognitive aspects of adult ADHD in Taiwanese population.