Attention-deficit/hyperactivity disorder (ADHD) is one of the most common childhood disorders. First described in 1798 by Alexander Crichton, ADHD became widely known outside the medical profession with the publication of the story of Fidgety Phil (‘Zappelphilipp’) in Heinrich Hoffman's book ‘Struwwelpeter’ in 1846. Since then, scientists and clinicians have been struggling to understand its causes. To date, there is neither a genetic test nor a brain scan to diagnose ADHD due to the fact that it is a heterogeneous collection of behaviours that appear to have different causes and symptoms. In view of the lack of an objective diagnostic method, the major difficulty that specialists face is to decide where to set the threshold between behaviours and states of mind that require medication or behavioural treatment and differences that can be left alone. The increased rate in diagnosis and stimulant use in ADHD recently raises several issues, notably, are we setting lower diagnostic thresholds because of societies’ intolerance of behaviours and impairments associated with ADHD? This article discusses some of the controversies in ADHD diagnosis and treatment, including many medical, social, and ethical aspects.