PROJECT SUMMARY Transgender and gender expansive (TGE) youth identify as a gender different from their sex at birth. Research tends to define this group based on high rates of sexually transmitted infections (STIs), sexual risk behaviors, violence exposures, and other health outcomes. Little work has used a supportive, resilience-based framework or a human-centered approach. We conducted preliminary qualitative/co-design studies to understand sexual health content needs and format/design preferences. Content areas recommended by TGE youth, their families, providers, and/or advocates include: a) Youth/ providers noted that puberty can produce dysphoria for TGE adolescents and that information/tools would be beneficial; b) Participants asked for non-judgmental information about STI risks and prevention; c) Youth/providers asked for content around contraception that clarifies that gender-affirming medical interventions do not prevent unintended pregnancies; d) Participants recommended destigmatizing and normalizing diversity in sexual attractions and desires; e) TGE youth raised disclosure of TGE identity as a unique challenge and asked for communication skills training to help them maintain agency over when and how to disclose; and f) Participants described difficulties navigating partner consent because it is often described in heteronormative, binary terms in sexual education classes. TGE youth also described favoring written materials for more fact-based content on contraception and STIs, interactive formats for content that requires personalization by gender and/or degree of medical transition, and multimedia approaches emphasizing lived experience perspectives for information around desire, gender identity disclosure, and consent. Participants also provided design guidance (e.g., use of a covert color palette that would not unwantedly disclose users’ transgender status in public) and specific features (e.g., blacklisting functions to protect the user from triggering content; robust search and filter system to easily locate information specific to an individual’s needs). Based on these themes, we co-designed a paper intervention prototype with TGE youth. In this proposal, we will engage a Youth Advisory Board and Community Consultants to co-design a fully functional online interactive sexual education tool (OISET) with TGE youth (Aim 1a) and conduct cognitive interviews to refine select survey tools and ensure gender-affirming intervention effect measurement in a future R01 (Aim 1b). We will then conduct an unbalanced, randomized controlled pilot study with 40 youth (30 intervention:10 control) to refine content and establish feasibility of the OISET and data collection protocols/procedures (Aim 2). Primary outcomes will be intervention usability/feasibility/appropriateness/ acceptability and study feasibility. We will collect baseline, post-intervention, and 3 month data on knowledge; general/sexuality-specific self-efficacy; partner communica...