Objective: Self-harm is common among adolescents and has been shown to be associated with a range of adverse outcomes in adulthood. Although many risk factors for self-harm have been identified, less is known about potential protective factors. This longitudinal study aims to i) identify protective factors for self-harm with and without suicidal intent in adolescence, and ii) identify protective factors that may reduce the risk of repetition of self-harm between adolescence and adulthood. Methods: Data were derived from the Avon Longitudinal Study of Parents and Children (ALSPAC): A large birth cohort study in the UK involving over 14,000 pregnancies. Participants were assessed for self-harm at several time points in adolescence and adulthood. Protective factors were assessed across development and categorised into individual, family, and peer-level. They include factors such as social communication, perceived school competence, self-worth, religion, and relationships with family and peers. Associations will be examined using regression models and will be adjusted for relevant confounders such as sex and socioeconomic position. Multiple imputation will be used to take account of missing data. Results: Data on self-harm is available for approximately 5,000 participants at age 16 years. The prevalence of self-harm at age 16 was 19%, with 7% reporting at least one suicide attempt. Regression analysis is currently underway to explore associations between protective factors and adolescent self-harm and identify factors that protect against self-harm continuity into adulthood. The findings of these analyses will be presented at the conference. Conclusion: Identifying factors that protect against self-harm onset and repetition will provide important information to inform the development of prevention programmes and promote resilience.