The impact of individual and psychosocial factors on drug treatment in childhood attention-deficit hyperactivity disorder (ADHD). The aim of this study is to provide knowledge concerning the relation between psychosocial and individual risk factors and their impact on long time effectiveness and compliance with drug treatment in childhood ADHD. The project makes use of systematically and prospectively collected data from a representative, consecutively recruited clinical cohort of 200 children, recently diagnosed with ADHD, who were closely monitored under standardized conditions during the first 12 weeks of Methylphenidate (MPH) treatment. We will use the existing prospective clinical data in this cohort and combine those with measurements concerning risk- and psychosocial factors derived from the Danish registries. Finally, we will follow the cohort after three years with respect to ADHD symptoms, quality of life, and treatment continuity. The latter will also combine direct information from questionnaires to parents and teachers as well as data derived from The Danish National Prescription Registry regarding ADHD medication which has been prescribed to, and purchased by the participants in the follow-up period.