Key Features The New South Wales Child Development Study (NSW-CDS) was established to enable an intergenerational life-course approach to identifying risk and protective factors for adolescent-onset mental health problems in an Australian state-based population cohort. New multi-agency linked administrative data for the child cohort (n = 91 597 children; 44 216 female) now span birth to ∼18 years (including birth, mortality, health, education, child protection, criminal justice and welfare records up to 2021/2022), with parental data obtained for ∼83% of the child cohort via births registered in NSW or perinatal records in NSW or the Australian Capital Territory. Attrition is limited to deaths and movement out of the jurisdictions of various record sources (e.g. state government or Australian Commonwealth). The added range of adolescent data provides new targets for investigation of outcomes in relation to developmental vulnerability at school entry (age 5–6 years; 2009 Australian Early Development Census), and mental health and wellbeing assessed via self-report survey in Year 6 (age 11–12 years; 2015 Middle Childhood Survey). Australian government data are governed by privacy laws that prohibit data sharing. To discuss potential collaborative projects, please contact Melissa Green.