Background. Life-space, a measure of movement through one's environment, may be viewed as one aspect of environmental complexity for older adults. We examined the relationship between life-space and subsequent change in cognitive function. Methods. Participants were 624 community-dwelling Medicare beneficiaries (49% African American) who completed in-home assessments at baseline and follow-up 4 years later. The Life-Space Assessment was used at baseline to measure extent, frequency, and independence of participants' movement within and outside the home. Cognitive decline was measured with the Mini-Mental State Examination (MMSE). Results. In a regression model adjusted for baseline MMSE, age, gender, race, residence (rural/urban), and education, greater life-space at baseline predicted reduced cognitive decline (β = -.177, p < .001). This association remained statistically significant in subsequent models that examined what proportion of the observed association was explained by baseline physical activity, physical function, vascular risk factors, comorbidity, and psychosocial factors. Physical function accounted for the largest proportion (37.3%) of the association between life-space and cognitive decline. There was no significant interaction between life-space and race, gender, or age in predicting cognitive decline. In a logistic regression analysis, participants in the highest quartile of life-space had 53% reduced odds of substantial cognitive decline (≥4 points on MMSE) compared to those in the lowest quartile. Conclusions. These preliminary findings suggest that life-space may be a useful identifier of older adults at risk for cognitive decline. Future research should investigate the potential reciprocal relationship between life-space and cognitive function as well as the interrelationship between these factors and physical function. Copyright 2008 by The Gerontological Society of America.