This study of institutional categorization reports an investigation of the practices, procedures and assumptions of psychiatric staff members when diagnosing ADHD. The main data upon which the study is based consist of transcribed audio recordings of meetings in the psychiatric clinic. Here children referred from primary schools on the suspicion of ADHD are attended to. The tools and procedures for gathering information are shown to produce decontextualized and individualizing representations of children's conduct. The evaluation against a number of norms is found to be central. Finally, the discussions at the central team conferences are shown to reveal the use of hypothesis testing structured around a number of dichotomies, where isolated aspects of the child's life are considered against each other as the source of the difficulties. Together, these practices have cumulative and profound consequences for how children's problems come to be understood as caused by a neurological condition.