In order to defend the diagnostic validity of ADHD, the specialized literature tends to use a historical argument, according to which its validity is unquestionable due to the fact that a number of medical sources have referred to ADHD for several hundred years. This proves that ADHD is not a contemporary creation. However, when investigating those same historical sources, it is possible to prove that these arguments are unfounded, which contributes even more to undermine this highly controversial psychiatric construct. This paper analyzes the three classic “milestones” of the so-called history or prehistory of ADHD: Alexander Crichton, Heinrich Hoffmann and George F. Still. Contrary to the claims of the dominant literature, ADHD is a modern invention and the use of these historical arguments reveals its mythical theoretical basis and lack of supporting arguments, which should be a cause for serious concern, due to the number of children being diagnosed and medicated for ADHD.