Attention Deficit Hyperactivity Disorder (ADHD) is an unsettled condition whose history is characterised by controversy among medical professionals. Its emergence has frequently been interpreted as an example of the growing 'medicalisation' of society and the individualisation of social issues. This article examines how groups representing children with ADHD in France and Ireland engage within this contested medical domain to develop different politics of knowledge around the disorder which become visible in their 'epistemic efforts'. These efforts emerge from, and enact, groups' understandings of ADHD as a condition, and frame their development of a politics of healthcare as a basis for articulating claims to appropriate services and treatment. We show how, in Ireland, organisations remain committed to a biomedical approach to ADHD, although their practical efforts are oriented towards complementing medication with nonpharmaceutical treatments. In France, the key parents' group opposes any paradigm that focuses exclusively on one aspect of the disorder, be it social, psychological or neurological; rather, it struggles to 'open up' the scientific domain of ADHD. Our empirical material therefore enables us to demonstrate patients' organisations' politics of knowledge as situated practices which aim to reshape the different networks of expertise on ADHD that exist in each country, and to explore medicalisation as a complex set of processes which is neither a solution to parents' problems, nor an end point for their actions.