Brain donation in studies on aging remains a critical pathway to discovering and improving preventive measures and treatments for Alzheimer's dementia and related disorders. Brain donation for research is almost exclusively obtained from non-Latinx Whites of higher socioeconomic status in the United States. Despite persistent efforts, it has been difficult to obtain consent for brain donation among diverse participants. Hence, our understanding of Alzheimer's dementia and related disorders remains incomplete. The purpose of this methodological paper was to propose and outline a two-phase sequential mixed-methods research study design to identify barriers and facilitators of brain donation among diverse older adults. The first phase will consist of qualitative focus groups using a three (participant minority status: African American, Latinx, or White of lower income) by two (participant brain donation decision: consented or declined) design. The second phase will include statistical analyses of quantitative measures of existing data representing categories of variables that may be associated with decision making regarding brain donation. Next steps must include conducting qualitative focus groups and subsequent data analyses, resulting in overarching themes. Afterward, qualitative themes will be operationalized using quantitative variables for statistical analyses. This proposed study design can provide the foundation for developing and implementing effective and culturally competent survey instruments, educational tools, and intervention strategies in an effort to facilitate brain donation among diverse older adults.