No representative population-based studies of youth in the United States exist on gender identity-related disparities in suicidal ideation or on factors that underlie this disparity. To address this, this study examined gender identity-related disparities in the prevalence of suicidal ideation; evaluated whether established psychosocial factors explained these disparities; and identified correlates of suicidal ideation among all youth and stratified by gender identity. Data were derived from the 2013 to 2015 California Healthy Kids Survey (CHKS; N= 621,189) and a weighted subsample representative of the Californian student population (Biennial Statewide California Student Survey [CSS], N= 28,856). Prevalence of past 12-month self-reported suicidal ideation was nearly twice as high for transgender compared with non-transgender youth (33.73% versus 18.85%; χ2= 35.48, p< .001). In fully adjusted models within the representative sample, transgender youth had 2.99 higher odds (95% CI 2.25-3.98) of reporting past-year suicidal ideation compared with non-transgender youth. Among transgender youth, only depressive symptoms (adjusted odds ratio 5.44, 95% CI 1.81-16.38) and victimization (adjusted odds ratio 2.66, 95% CI 1.26-5.65) remained significantly associated with higher odds of suicidal ideation in fully adjusted models. In multiple mediation analyses, depression attenuated the association between gender identity and suicidal ideation by 17.95% and victimization by 14.71%. This study uses the first representative population-based sample of youth in the United States that includes a measurement of gender identity to report on gender identity-related disparities in suicidal ideation and to identify potential mechanisms underlying this disparity in a representative sample.