BACKGROUND: Lesbian, gay and bisexual (LGB) young people's increased risk of self-harm, suicidal attempts and suicide compared with heterosexual youth is well established. The current study sought to examine whether these findings also apply to the trans (T) population and which factors act as additional risk or protective factors. METHODS: In a national cross-sectional survey, 3713 LGBT adolescents, aged 11-19 years, reported on their own history of self-harm, suicidal ideation and suicide attempts, as well as their experiences of school and homophobic, biphobic and transphobic bullying. Logistic regressions tested the association between risk and protective factors on self-harm, suicidal ideation and suicide attempts. RESULTS: A high proportion of the sample reported self-harm (65.3%), suicidal ideation (73.8%) and suicide attempts (25.7%). Demographic risk factors included identifying as female, non-binary or trans and being from a low-income background. Bullying and online bullying were associated with an increased risk for each outcome, and positive school experience was associated with a reduced risk for each outcome. CONCLUSIONS: Consistent with minority stress theory, the study found high rates of mental health problems within LGBT youth. Interventions focused on improving young people's experiences in schools appear useful targets to help improve mental health outcomes.