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The current population of older Americans has accumulated substantial lifetime lead doses, which raises concern about the possibility of adverse cognitive outcomes. We evaluated whether cumulative lead dose from environmental exposures is associated with cognitive function and decline, and whether such effects are persistent, reversible, or progressive.We used longitudinal linear modeling to evaluate associations of tibia lead concentration with cognitive function and decline in sociodemographically diverse, community-dwelling adults aged 50–70 years who were randomly selected from neighborhoods in Baltimore. Six summary measures of cognitive function were created from standard tests in the following domains: language, processing speed, eye-hand coordination, executive functioning, verbal memory and learning, and visual memory.The mean (SD) tibia lead level was 18.8 (11.6) μg/g. In models adjusted for demographic characteristics, socioeconomic status (SES), and race/ethnicity, higher tibia lead was associated with a progressive decline in eye-hand coordination. Tibia lead was associated with persistently impaired cognitive function in all 6 domains, although these associations weakened after increasing covariate control. In fully adjusted stratified analysis among white persons, persistent effects were apparent in eye-hand coordination, executive functioning, and verbal memory and learning.The study presents the strongest evidence to date of the effects of cumulative lead dose on adult cognitive function independent of SES. The study population was relatively young and the average total duration of follow-up short (<30 months); these findings may represent the lower bound of the impact of cumulative lead dose on cognitive function of older adults.