Project Summary. In times of serious illness or at the end of life, many Americans receive unwanted care, including life- prolonging and painful interventions, and die in institutional settings. Advance care planning (ACP) permits individuals to communicate their preferences should they become unable to make decisions regarding their own medical care due to physical, cognitive, and/or communicative impairments. ACP improves the concordance between persons’ wishes and the care they receive, and increasing the utilization of ACP can yield benefits to patients, kin and families, and the health care system. Very little is known regarding ACP disparities and predictors among midlife and older adult gay, bisexual, and other men who have sex with men (GBMSM). Existing ACP research has numerous gaps, and GBMSM have distinct life experiences that limit generalizing from existing data regarding ACP behaviors in the general population. It is not known whether there are disparities in ACP across sociodemographic groups such as race, ethnicity, and socioeconomic status among GBMSM. There is also a need to identify psychosocial factors that may influence ACP behaviors among GBMSM. This research will examine formal and informal dimensions of two ACP behaviors (health care proxy, advance directives) using secondary data analyses from the Multicenter AIDS Cohort Study, a longitudinal study of GBMSM with extensive data on sociodemographics, health and health care, and psychosocial factors. The specific aims are to 1) Describe the types and extent of advance care planning (ACP) among midlife and older adult GBMSM, and assess potential disparities across sociodemographic groups; 2) Assess differences in the prevalence of ACP across longitudinal health indicators, and longitudinal health care access and utilization; and 3) Test associations between psychosocial factors and ACP, and whether these associations differ across HIV serostatus groups. This research is critical to understanding ACP among older GBMSM, developing culturally-appropriate models of ACP, and addressing within-group disparities. Improving rates of ACP among GBMSM supports high quality care that is concordant with patients’ wishes during severe illness or at the end of life. These findings will also move the broader field of ACP research forward by virtue of examining factors that are understudied in ACP research more generally (e.g., psychosocial factors).