This is a prospective, long-term, observational study of routine clinical care. The study measurements will be integrated into the clinical assessment and follow-up procedures of the outpatient services under the Provincial ADHD Program. The study is designed for systematic follow-up of children and adolescents, diagnosed with ADHD irrespective of comorbidity or whether they elect to receive medication treatment. Evaluations occur every 6 months for 24 months. The population to be examined is children and adolescents with a diagnosis of ADHD, aged 6 to 18 inclusive (at baseline), referred to the Provincial ADHD Program for clinical assessment. No studies have been conducted that have evaluated the outcome of core ADHD symptoms in a clinic setting. Metaanalysis of clinical trials of medication treatment for ADHD have suggested an effect size of approximately 0.8. Because of the heterogeneity of the clinic sample, a much lower effect size can be anticipated. Two hundred patients will be enrolled in this study with primary measure of effectiveness being change in ADHD symptoms.