INTRODUCTION: Circulating neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) have been independently associated with dementia risk. Their additive association, and their associations with dementia-specific mortality, have not been investigated. METHODS: We associated serum NfL, GFAP, total tau, and ubiquitin carboxyl-terminal hydrolase-L1, measured in 1712 dementia-free adults, with 19-year incident dementia and dementia-specific mortality risk, and with 3-year cognitive decline. RESULTS: In adjusted models, being in the highest versus lowest tertile of NfL or GFAP associated with a hazard ratio (HR) of 1.49 (1.20–1.84) and 1.38 (1.15–1.66) for incident dementia, and 2.87 (1.79–4.61) and 2.76 (1.73–4.40) for dementia-specific mortality. Joint third versus first tertile exposure further increased risk; HR = 2.06 (1.60–2.67) and 9.22 (4.48–18.9). NfL was independently associated with accelerated cognitive decline. DISCUSSION: Circulating NfL and GFAP may, independently and jointly, provide useful clinical insight regarding dementia risk and prognosis.