PROJECT SUMMARY/ABSTRACT The long-term goal of this project is to increase the trustworthiness of health care providers and institutions and decrease the rates of medical mistrust among homeless-experienced older adults, thereby, improving health outcomes. The proposal seeks to renew 2AG041860, “Aging Among the Homeless: Social Isolation, Function and Institutional Care” and continue the Health Outcomes in People Experiencing Homelessness in Older Middle agE (HOPE HOME) study, which recruited and followed a cohort of 450 homeless adults age 50 or older. Approximately half of all homeless adults are age 50 or older; this trend is expected to continue. HOPE HOME participants have poor health, including physical health problems, geriatric conditions, and functional impairments similar to housed individuals in their 70s and 80s. Black Americans, LGBTQ+ individuals, and those with mental health problems and/or substance use disorders are overrepresented in the homeless population, including in the HOPE HOME study sample. Individuals with these identities may experience discrimination and stigma, which influence medical mistrust. Mistrust may be a barrier to health care utilization and related to poor health outcomes in older homeless adults; little is known about this association. We propose to recruit an additional 150 HOPE HOME participants to replace those who have died or been lost to follow-up, and to follow the cohort for 54 months with nine semi-annual visits for structured interviews. We will recruit a sub-sample of 30 participants for in-depth qualitative interviews and 20 of those for clinical observation to understand the factors associated with medical mistrust and its dynamic nature. We will recruit 20 key informants who work in settings that serve homeless older adults for in-depth qualitative interviews. Study visits for participants will take place at an administrative building belong to Lifelong Medical, a FQHC which serves older homeless adults. Participant observations will take place at local clinics and health care institutions. Trained interviewers, under the supervision of study investigators, will administer structured interviews to assess key variables and study investigators with research personnel will conduct participant observation of primary care visits. A Community Advisory Board, composed of community and policy leaders in homelessness and study participants, will work with the study team to guide study development and translate the findings into a toolkit, practice, and policy. Study findings will contribute to the development of clinical, programmatic, and policy recommendations summarized in a toolkit aimed to increase trustworthiness of health care institutions.