Young Minds Matter: The second Australian Child and Adolescent Survey of Mental Health and Wellbeing provides updated national prevalence estimates of mental disorders in children and adolescents and measures the burden and impact of these disorders and the use of services and unmet need for services in the health and education sectors. The field work for Young Minds Matter included face-to-face interviews with the primary carer of 6,310 children and adolescents aged 4–17 years who were randomly selected from across Australia. This article describes the survey, the response rates achieved and the representativeness of the sample.