Project Summary/Abstract: This application is being submitted in response to NOT-DA-21-044: Administrative Supplements to Support Research on Health Equity in NIDA-funded Grant Awards. The parent K23 award seeks to improve the delivery of coordinated chronic disease management for older adults with substance use disorder who receive care in addiction treatment settings. The compound stigma of aging and substance use disorder places older adults with opioid use disorder (OUD) at high risk for multiple chronic diseases, geriatric conditions, disorganized clinical care, and high acute care utilization. However, these outcomes are not experienced equally among older adults with OUD, given the lifelong experience of discrimination, racism, and barriers to care. Furthermore, delivering geriatric-based interventions into substance use treatment settings, which is the goal of the parent K23 to develop, must consider the language and cultural contexts of diverse older adults with OUD. This administrative supplement proposes a mixed methods research study to improve the understanding of the health disparities faced by older adults with OUD. The information gained from the proposed study will better inform interventions to achieve health equity in this diverse population. The first part of this study will involve the use of non-public datasets from the California Office of Statewide Health Planning and Development (OSHPD) to quantitatively measure the differences in the prevalence of and risk factors for high utilization of acute healthcare, high medical costs, and multiple chronic conditions among older adults with OUD by race and ethnicity (Aim 1). Guided by Aim 1 and The National Institute on Minority Health and Health Disparities Research Framework, we will increase the planned enrollment of the parent K23 qualitative study to focus specifically on Spanish-speaking older adults with OUD who identify as Hispanic/Latinx. This qualitative study will examine the contextual barriers, attitudes, acceptance, and feasibility of integrating geriatric and chronic disease models of care with treatment for OUD and how this differs from non-Spanish speaking populations in opioid treatment programs (Aim 2). Findings from this supplement will inform efforts to widely integrate evidence-based interventions of geriatric-based chronic disease assessment and management into existing substance use treatment programs for diverse older adults with OUD.