ABSTRACT The purpose of this epidemiologic study is to determine if sensory changes (hearing, vision, olfaction) and an emerging biomarker of aging (PhenoAge) measured in midlife are strong predictors of long-term risk for early Alzheimer’s disease and related dementias (ADRD), and to study the shared etiology of co-occurring sensory and cognitive changes. Subjects are previous participants in a prospective longitudinal cohort study, the Beaver Dam Offspring Study (BOSS) and were 21-84 years of age at the baseline examination (2005-2008). The proposed study (BOSS–Neurocognitive Aging Study) will apply standardized protocols used in the BOSS baseline, 5-year and 10-year follow-up examinations including a hearing evaluation (otoscopy, audiometry and word recognition in quiet and in competing message), eye examination (refraction, visual acuity and contrast sensitivity) and olfaction testing (San Diego Odor Identification Test) and conduct an extended cognitive test battery (Trail Making Test, Auditory Verbal Learning Test, Verbal Fluency Test, Digit Symbol Substitution Test, Digit Span, Stroop Test, Mini-Mental State Examination). We will further enhance the evaluation of early ADRD status by incorporating medical records, caregiver interviews and blood-based biomarkers of AD and neurodegeneration (amyloid b40, amyloid b42, total Tau and phosphorylated Tau) in a clinical review that will be conducted by a multidisciplinary neurocognitive expert panel in a diagnosis consensus conference. Cardiovascular risk factors will be assessed and standardized questionnaires on medical history, medication usage and lifestyle and environmental factors will be completed. We will measure longitudinal changes in PhenoAge using new and stored baseline blood samples. The proposed epidemiological study will provide important information about early biomarkers for the risk of developing cognitive decline and early ADRD and will inform about relationships between changes in sensory and cognitive function. This will contribute to developing clinically useful methods to identify high-risk people in midlife and to understanding the shared etiologies of sensory and cognitive changes. This project’s results will inform about potential pathways for prevention of ADRD and the promotion of healthy brain aging.