Background Research suggests that lesbian, gay and bisexual (LGB) adolescents have a higher risk of suicidal behaviours than their heterosexual peers, but little is known about specific risk factors. Alms To assess sexual orientation as a risk factor for suicidal behaviours, and to identify other risk factors among LGB adolescents and young adults. Method A systematic search was made of six databases up to June 2015, including a grey literature search. Population-based longitudinal studies considering non-clinical populations aged 12-26 years and assessing being LGB as a risk factor for suicidal behaviour compared with being heterosexual, or evaluating risk factors for suicidal behaviour within LGB populations, were included. Random effect models were used in meta-analysis. Results Sexual orientation was significantly associated with suicide attempts in adolescents and youths (OR=2.26, 95% CI 1.603.20). Gay or bisexual men were more likely to report suicide attempts compared with heterosexual men (OR=2.21, 95% Cl 1.21-4.04). Based on two studies, a non-significant positive association was found between depression and suicide attempts in LGB groups. Conclusions Sexual orientation is associated with a higher risk of suicide attempt in young people. Further research is needed to assess completed suicide, and specific risk factors affecting the LGB population.