BackgroundGambling among adolescents is associated with gambling disorder in adulthood. This study investigated factors associated with gambling and excessive gambling in adolescents. MethodsThis secondary analysis of the cross-sectional European School Survey Project on Alcohol and Other Drugs (ESPAD) used nationally representative data from the Irish cohort of the 2019 ESPAD wave. Data were collected between March and May 2019. We included 1949 students aged 15–16 years (946 [48·5%] male, 1003 [51·5%] female), with a response rate of 85%. We calculated past year gambling prevalence as the rate of those who had gambled for money on at least one of four games of chance (slot machines, cards or dice, the lottery, betting on sports or animals) in the past 12 months. An adapted version of the three-item Consumption Screen for Problem Gambling was used to identify excessive gambling (score ≥4). We carried out descriptive and logistic regression analyses using binary covariates with Stata v16.1. We included 19 variables in the multivariable analysis. Ethics approval was granted by Dublin Institute of Technology's Ethics Committee. Non-consent forms were issued to all parents to opt out. FindingsOverall, 447 (23%) of 1949 students gambled in the past year, of whom 45 (10%) engaged in excessive gambling. Using a mutually adjusted multivariable logistic regression analysis, past year gambling was associated with alcohol use (adjusted odds ratio [aOR] 1·6, 95% CI 1·1–2·2), experiencing serious arguments (aOR 1·4, 1·1–1·9), and trouble with the police (aOR 1·9, 1·2–2·8). Female gender was a protective factor (aOR 0·6, 0·4–0·9). In the univariable analysis, excessive gambling was associated with gaming (OR 2·3, 1·0–5·1), tobacco use (2·1, 1·1–4·2), e-cigarette use (2·1, 1·1–4·1), heavy episodic drinking (2·7, 1·4–5·1), trouble with the police (2·8, 1·5–5·4, p<0·01), and deliberately hurting themselves (2·8, 1·4–5·6). Female gender (OR 0·3, 0·1–0·6) and social media use (0·4, 0·2–0·8) were protective factors. Excessive gambling was also associated with betting on sports and animals (OR 3·6, 1·6–8·4), slot machines (2·9, 1·5–5·8), card or dice (2·4, 1·2–4·6), and online gambling (4·2, 2·0–8·0). InterpretationA large proportion of 15–16 year olds in Ireland have gambled for money in the past year, with one in ten of those having engaged in excessive gambling. This number is likely to be underestimated due to recall and social desirability bias. Reducing the availability, access, and appeal of gambling products in Ireland should be addressed through ongoing gambling reform. FundingInstitute of Public Health.