PROJECT SUMMARY Bisexual young adults report worse health behaviors than both heterosexual and lesbian/gay young adults due to experiences of pervasive stigma-based sexual minority stress. However, little research has considered the potential mitigating or exacerbating role of romantic relationship dynamics on the association between stigma and health behaviors among bisexual young adults. The potential for romantic relationships to be protective for health is complicated for bisexual young adults, whose sexual identity is defined by the ability to enter into same- or different-sex relationships. Identifying modifiable relationship dynamics that influence the impact of stigma on the health of bisexual young adults can illuminate pathways of health across the lifespan and reduce bisexual health disparities. The proposed project will assess how sexual minority stigma relates to health behavior, the moderating role of positive and negative aspects of relationship dynamics, and whether/how these associations differ for bisexual young adults in same- and different-sex relationships. We will collect baseline and 14 days of daily diary data from 1,000 young adults (250 bisexual women in a same-sex relationship, 250 bisexual men in a same-sex relationship, 250 bisexual women in a different-sex relationship, and 250 bisexual men in a different-sex relationship) between the ages of 18-26 who have been with their romantic partner for at least four months. We will conduct cross-lagged multilevel modeling analyses to (1) determine how sexual minority and bisexual-specific stigma influences the health behaviors of bisexual young adults; (2) identify positive and negative relationship dynamics that moderate the association between stigma and health behaviors; and (3) examine how the daily associations between stigma, relationship dynamics, and health differ for young bisexual women and men in same- and different-sex relationships. Results will have significant implications for programs, practices, and policies aimed at improving relationships and eliminating health disparities among bisexual populations.