PROJECT SUMMARY/ABSTRACT The overall goal of this K23 proposal is to provide Olivia Van Gerwen, MD, MPH with the necessary mentorship and career development to become an independent investigator whose work will contribute to decreasing sexual health disparities faced by transgender and gender diverse (TGD) populations. The focus of her research will be on the vaginal health of transgender men (TGM). Testosterone can negatively impact the vaginal health of TGM by thinning the vaginal epithelium and leading to atrophic vaginitis and vaginal dysbiosis. In addition to symptoms (e.g., irritation, discharge, odor, dyspareunia), these changes can increase the risk of HIV and sexually transmitted infection (STI) acquisition. Despite their significance, vaginal symptoms and infections are poorly characterized in TGM. This population is underserved and have limited engagement with sexual health services, largely due to discrimination from and mistrust of the medical establishment. Since many TGM do not undergo bottom surgery, vaginal health is an important sexual health consideration. However, there is a critical knowledge gap in how testosterone-prescribing healthcare providers should assess these symptoms (both through history-taking and clinical specimen collection) in an affirming manner. Community-informed approaches are necessary to promote more satisfactory sexual healthcare experiences for TGM and, thus, improve sexual health outcomes. In this study, we will perform mixed methods research to inform the development of clinical tools for use by healthcare providers to collect both vaginal history data and clinical specimen data. This research will allow providers to better assess and manage vaginal symptoms that TGM experience, ultimately optimizing the vaginal health of this population and mitigating the impacts of testosterone. Aim 1: Develop a survey instrument measuring the vaginal health of TGM on testosterone for use in clinical settings. Aim 2: Examine the psychometric properties of the items to finalize the instrument. Aim 3: Characterize the acceptability and feasibility of vaginal specimen self-collection and quantify the frequency of bacterial vaginosis (BV) among TGM on testosterone. With guidance from my mentorship and advisory team, I have created a training plan that will allow me to gain expertise in mixed methods research, community engagement, and sexual and vaginal health outcomes research through didactic coursework, hands-on training, and expert mentorship. Upon completion of the research aims in this proposal, I will develop an R01 proposal which will utilize the tools and data generated to develop a multi-level intervention focused on improving the patient-provider experience for TGM with vaginal health needs.