The purpose of this study was to ascertain the prevalence and correlates of self-harm among young people in detention in Australia. The sample included 215 (177 male; 38 female) young people who were in youth detention in the state of Victoria, Australia. Participants were administered a series of questionnaires related to self-harm, mental health, socio-environmental experiences and behaviours. Overall, one-third (33%) of the sample reported previous self-harm and 12% reported at least one suicide attempt. In a multivariate logistic regression analysis, a history of childhood trauma, contact with mental health services, and low educational interest significantly increased the likelihood of self-harm. Young people who reported a suicide attempt scored significantly higher on the measure of childhood trauma than did youth who had engaged in non-suicidal self-harm. Findings demonstrate a strong connection between childhood traumatic experiences and suicidal behaviours for youth in detention. Trauma histories and mental health concerns must be considered when identifying youth at increased risk of self-harm.