Project Summary Suicide is the second leading cause of death among youth ages 10-24, constituting a major public health crisis. Adolescence is also associated with the onset of non-suicidal self-injury (NSSI), which often co-occurs with suicidal thoughts and behaviors (STBs). Importantly, sexual minority (e.g., gay, lesbian, bisexual) adolescents are at increased risk for STBs/NSSI compared to their heterosexual peers. As such, there is a critical need to identify risk factors for STBs/NSSI among sexual minority adolescents. Interpersonal stress, particularly rejection, can have major consequences for mental health during adolescence given the increased salience of interpersonal relationships during this developmental period. Despite support for rejection as a risk factor for STBs/NSSI among adolescents, there are critical gaps in our understanding of these associations including: 1) most research in this area has been cross-sectional, limiting our understanding of the extent to which rejection is associated with changes in STBs/NSSI over time; 2) in addition to experiences of rejection, the extent to which an individual anticipates and worries about future rejection (rejection sensitivity [RS]) may also contribute to STBs/NSSI, but research has yet to examine RS in relation to STBs/NSSI; and 3) sexual minority youth are exposed to unique forms of interpersonal stress related to their stigmatized identities, including being rejected by their peers and parents, but no studies to date have examined identity-specific rejection and RS in relation to STBs/NSSI among sexual minority adolescents. To address these limitations, the goals of the current study are to examine sexual minority status as a moderator of the longitudinal associations between rejection/RS and STBs/NSSI among adolescents, and to examine the associations between daily experiences of sexual orientation-related rejection/RS and STBs/NSSI among sexual minority adolescents. These goals will be accomplished by leveraging data from two NIMH-funded R01s (PI: Liu; Co- Sponsor). As part of the parent studies, psychiatrically-hospitalized adolescents will complete measures of rejection, RS, STBs, and NSSI at baseline and six-months post-hospitalization. They will also complete measures of STBs and NSSI on a daily basis for one-month beginning upon discharge from the hospital. Consistent with NIMHD’s priorities to elucidate interpersonal and sociocultural influences on behavioral disparities among minorities, this project will leverage longitudinal data and real-time monitoring of daily experiences to advance our understanding of risk for STBs/NSSI among sexual minority adolescents and to inform tailored suicide prevention efforts. This award will also support the applicant’s training in adolescent STBs/NSSI, sexual minority health, and intensive longitudinal methods. Findings from the current study will be used to inform a proposal for a K-award focused on developing an intervention to reduc...