Purpose: This study aimed to estimate the prevalence of poor mental health, repetitive self-harm, and suicide attempts among adolescents in Ireland between 2018 and 2023; to identify demographic groups at elevated risk; and to assess changes in these outcomes across the time period.

Methods: The Planet Youth survey is a repeated cross-sectional study in which 21,340 secondary school students aged 15–19 years and 588 early school leavers were surveyed across seven local authorities in Ireland. Participants anonymously self-reported mental health status, lifetime repetitive self-harm, and suicide attempts. We used multilevel logistic regression, accounting for school and regional clustering, to estimate population prevalence rates, identify risk groups, and assess temporal trends. Young people with lived experience of adolescent mental health problems provided their insights on survey methodology and findings.

Results: Averaged across the 5-year period, 19.6% reported poor mental health, 12.1% repetitive self-harm, and 8.4% a lifetime suicide attempt. Transgender/gender-diverse adolescents and early school leavers were most likely to report these outcomes. By 2022/23, rates of poor mental health and suicide attempt had returned to pre-COVID levels, however, rates of repetitive self-harm continued to rise. Lived experience reflections highlighted the contributions of service inaccessibility and the role of cultural trends.

Conclusion:Findings highlight high levels of psychological distress among Irish youth. There was significant heterogeneity of risk across subgroups, with implications for both universal and targeted interventions. Continued surveillance of adolescent mental health and the expansion of accessible youth mental health services remain key priorities.