ABSTRACT Approximately 5.7 million Americans have dementia. Alzheimer’s dementia accounts for the majority of cases. The rising prevalence and impact of dementia in the US, coupled with a lack of effective treatments to prevent, cure, or slow dementia progression, have galvanized an urgent need to identify modifiable risk factors. One may be obstructive sleep apnea (OSA). This highly underdiagnosed and consequential sleep disorder affects at least 24% of older Americans. Although emerging evidence has linked OSA to cognitive impairment and dementia incidence, existing reports have insufficiently examined potential key confounders as well as biologically relevant biomarkers that may influence this relationship. Furthermore, little research has focused on the effects of OSA treatment with positive airway pressure therapy (PAP) on risk for development of dementia. Recent data from the investigators demonstrate a lower incidence of Alzheimer’s dementia among Medicare beneficiaries with OSA who are treated with PAP, compared to non-PAP users. This suggests a protective role for PAP use on dementia risk in OSA-affected older adults. Data from the investigators also has shown sex disparities in OSA treatment. The vulnerability of women to both Alzheimer’s dementia and OSA under-treatment further highlights the question of whether OSA is a risk factor for Alzheimer’s dementia. Therefore, the overarching goal of this project is to assess the longitudinal impact of OSA and PAP on cognitive outcomes among older women and men, and to deconstruct unexplored pathways between pathological sleep and dementia. This will be accomplished by leveraging objective cognitive, sleep, health, and biomarker data that are collected biennially from the Health and Retirement Study. Data from this nationally representative, multi-ethnic longitudinal cohort of older adults will be harmonized with Medicare claims data to create a large dataset uniquely suited to address critical questions that would be unfeasibly expensive to investigate in a prospective manner. Findings from this study will provide new insight into sleep- based targets to reduce cognitive morbidity of older women and men; inform more targeted randomized clinical trials; and foster efforts to identify older individuals most likely to benefit from evaluation and treatment for sleep disorders.