Growing up in Ireland is the national longitudinal study of children in the Republic of Ireland. Funded by the Department of Children and Youth Affairs (DCYA), the project is overseen and managed by the DCYA in association with the Central Statistics Office. The child cohort was recruited in 2007, when 8568 nine-year-olds were interviewed. Just over 7400 young people were re-interviewed at 13 years of age (between August 2011 and February 2012) and just over 6200 participated again at 17–18 years (between 2015 and September 2016). This article highlights key findings on alcohol, tobacco and illicit substance use in this cohort using information collected during the third wave of the study.¹ The data were collected in home-based, face-to-face interviews.