Frailty is a common clinical syndrome in older adults that carries an increased risk for poor health outcomes. Little is known about the behavioral antecedents of frailty. In this study, the authors hypothesized that constriction of life space identifies older adults at risk for frailty, potentially a marker of already-decreased physiologic reserve. The authors analyzed the 3-year (1992-1995) cumulative incidence of frailty using a previously validated clinical phenotype in relation to baseline life-space constriction among 599 community-dwelling women aged 65 years or older who were not frail at baseline. Frailty-free mortality (i.e., death prior to observation of frailty) was treated as a competing risk. Multivariate survival models showed that, compared with women who left the neighborhood four or more times per week, those who left the neighborhood less frequently were 1.7 times (95% confidence interval: 1.1, 2.4; p < 0.05) more likely to become frail, and those who never left their homes experienced a threefold increase in frailty-free mortality (95% confidence interval: 1.4, 7.7; p < 0.01), after adjustment for chronic disease, physical disability, and psychosocial factors. Together, these data suggest that a slightly constricted life space may be a marker and/or risk factor for the development of frailty that may prove useful as a screening tool or a target of intervention.