The article elaborates the theoretical and methodological foundations of a Foucauldian-inspired critical ethnographic investigation of Attention Deficit Hyperactivity Disorder (ADHD). The aim was to consider ADHD from outside its dominant biomedical explanation as a means of problematizing the increasing usage within schools and health services. The investigation targeted the conditions that made it possible to "say" and "do" ADHD, for it to be "enacted" by various professionals. Thus, the investigation does not to engage with ADHD as a 'real' condition, but reconnects wider historic, social, political, institutional and discursive events within and across apparatuses of health and education that were influential in the emergence of a 'treatment' approach to ADHD. The approach, instead of 'treating' a 'real' condition, legitimated inscription of the biomedical explanation, individualized an array of difficulties as 'symptoms', and allowed for the governance of young people through psychostimulant medication.