Sexual minority (SM) youth experience a greater mental health burden compared with their heterosexual peers. This study aimed to characterize mental health disparities among SM compared with non-SM youth, test main and interactive associations of SM identity and stressors targeting SM youth at the individual level (interpersonal SM discrimination) and structural level (state-level structural SM stigma) with youth mental health, and explore the contribution of interpersonal SM discrimination to the mental health burden of SM youth. Participants included 11,622 youth (ages 9-13; 47.6% assigned female at birth) from the Adolescent Brain Cognitive Development (ABCD) Study. Linear mixed-effects models tested main and interactive associations of SM identity, interpersonal SM discrimination, and structural SM stigma with mental health measures (self-reported overall psychopathology, suicidal ideation, and suicide attempts), adjusting for demographics and other interpersonal stressors not specific to SM (other discrimination types, peer victimization, and cyberbullying). Longitudinal mediation models tested whether interpersonal SM discrimination mediated the associations between SM identity and mental health measures. SM youth (n= 1,051) experienced more interpersonal SM discrimination and overall psychopathology compared with their non-SM peers (n= 10,571). Adjusting for demographics, there were significant associations (main effects) of interpersonal SM discrimination and structural SM stigma with overall psychopathology. When further adjusting for other non-SM-related stressors, the main effect of structural SM stigma was no longer significant. Interpersonal SM discrimination was also significantly associated with suicidal ideation and attempt, accounting for demographics, while structural SM stigma was not. Accounting for both demographics and other non-SM stressors, there was a significant interaction between SM identity and structural SM stigma in association with psychopathology (p= .02), such that, compared with their peers, SM youth showed a greater association between structural SM stigma and psychopathology. Longitudinal mediation revealed that interpersonal SM discrimination was a significant mediator explaining approximately 10% to 15% of the variance of the pathways between SM identity and all mental health outcomes. Results delineate contributions of interpersonal discrimination and structural stigma targeting SM youth to their heightened mental health burden in early adolescence. These findings underscore the need to address microlevel and macrolevel SM discrimination and structural stigma when caring for this population. We worked to ensure sex and gender balance in the recruitment of human participants. We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented racial and/or ethnic groups in science. We actively worked to promote sex and gender balance in our author group. The author list of this paper includes contributors from the location and/or community where the research was conducted who participated in the data collection, design, analysis, and/or interpretation of the work. While citing references scientifically relevant for this work, we also actively worked to promote sex and gender balance in our reference list.