Thesis advisor: Kevin J. Mahoney / Lesbian, gay, bisexual, and transgender (LGBT) older adults in the U.S. face disproportionate risk of increased health and mental health problems as compared to their non-LGBT counterparts. Experiences of harassment, discrimination, and violence due to sexual orientation and gender identity (SOGI) contribute to the chronic stresses associated with being a sexual and/or gender minority. LGBT older adults may avoid or delay needed services in later life, rendering them invisible to health care providers (HCPs) if they do not disclose SOGI and if providers do not ask. This three-paper dissertation explored LGBT older adults' invisibility and outness in aging services. Paper 1 investigated gerontological social workers' biopsychosocial assessment practices to understand how they became aware of clients' SOGI; assessment forms were analyzed and qualitative interviews with social workers were conducted, showing that social workers did not have a systematic way of learning about clients' SOGI. Paper 2 was a quantitative analysis of survey data from 129 LGBT older adults that showed an association between experiences of SOGI-based discrimination/violence after age 50 and not disclosing SOGI to HCPs and having avoided using aging services for fear of coming or being out. Paper 3 was a qualitative analysis of interviews with 22 LGBT older adults that sought to understand how they disclosed SOGI to HCPs. Those who disclosed did so without being asked, because of health conditions, after having sought out an LGBT /LGBT-friendly provider, or after being asked about their sex and/or love lives. Paper 3 findings offered practice and environmental changes that could increase LGBT older adults' SOGI disclosure to HCPs. This dissertation provides suggestions for social work policy, practice, and research aimed at supporting gerontological social workers in learning about their clients' SOGI in an effort to address health disparities among LGBT older adults / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Social Work. / Discipline: Social Work.