As people age, they become more dependent on their local communities, especially when they are no longer able to drive. Uneven or discontinuous sidewalks, heavy traffic, and inaccessible public transportation, are just some of the built environment characteristics that can create barriers for outdoor mobility in later adulthood. A small body of literature has been investigating the role of the built environment on disability, but has been limited to cross-sectional analyses. The purpose of this paper is to further advance this area of research by examining the role of the built environment on long-term trajectories of mobility disability in a national sample of American adults (age 45+) followed over a 15-year period. Using multilevel logistic growth curve models with nationally representative data from the Americans' Changing Lives Study (1986-2001), we find that trajectories of mobility disability are steeper in older age groups. Women and those with lower education had a higher odds of mobility disability over time. The presence of just one chronic health condition doubled the odds of mobility disability at each of the four study waves. Among older adults (age 75+), living in neighborhoods characterized by more motorized travel was associated with an odds ratio for mobility disability that was 1.5 times higher in any given year than for older adults living in environments that were more pedestrian friendly. These results suggest that the built environment can exacerbate mobility difficulties for older adults. When considering ways to minimize disability as the population ages, simple changes in the built environment may be easier to implement than efforts to change risk factors at the individual level.