Attention deficit hyperactivity disorder (ADHD) has considered as a condition that is observed not only among children, but also among adults. ADHD observed among adults is diagnosed based on the assumption that it is the same condition as childhood-onset ADHD, whose etiology is found in neurodevelopmental disorder.
 On the other hand, there are concerns regarding the current concept of ADHD with onset in childhood and ADHD with onset in adulthood being regarded as the same entity, and hence being diagnosed and treated accordingly without sufficient investigation into whether adult-onset and childhood-onset ADHD are indeed the same etiology. Recent long-term cohort studies from New Zealand, the United Kingdom and Brazil suggested that childhood-onset ADHD and adulthood-onset ADHD may not necessarily lie on a continuum. These cohort studies have strong implications for the concept and diagnosis of ADHD. This report gives an overview of these three recently reported cohort studies while examining their significance and limitations, and discussing problems that adulthood-onset ADHD presentation.
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