BACKGROUND: Societies face the challenge of keeping people active as they age. Walkable neighborhoods have been associated with physical activity, but more rigorous analytical approaches are needed. OBJECTIVES: We used longitudinal data from adult residents of Brisbane, Australia (40 - 65 years of age at baseline) to estimate effects of changes in neighborhood characteristics over a 6-y period on the likelihood of walking for transport. METHODS: Analyses included 2,789 - 9,747 How Areas Influence Health and Activity (HABITAT) cohort participants from 200 neighborhoods at baseline (2007) who completed up to three follow-up questionnaires (through 2013). Principal components analysis was used to derive a proxy measure of walkability preference. Environmental predictors were changes in street connectivity, residential density, and land use mix within a onekilometer network buffer. Associations with any walking and minutes of walking were estimated using logistic and linear regression, including random effects models adjusted for time-varying confounders and a measure of walkability preference, and fixed effects models of changes in individuals to eliminate confounding by time-invariant characteristics. RESULTS: Any walking for transport (vs. none) was increased in association with an increase in street connectivity (+ 10 intersections, fixed effects OR = 1: 19; 95% confidence interval (CI): 1.07, 1.32), residential density (+ 5 dwellings/hectare, OR = 1: 10; 95% CI: 1.05, 1.15), and land-use mix (10% increase, OR = 1: 12; 95% CI: 1.00, 1.26). Associations with minutes of walking were positive based on random effects models, but null for fixed effects models. The association between land-use mix and any walking appeared to be limited to participants in the highest tertile of increased street connectivity (fixed effects OR = 1: 17; 95% CI: 0.99, 1.35 for a 1-unit increase in land-use mix; interaction p-value = 0: 05). CONCLUSIONS: Increases in street connectivity, residential density, and land-use heterogeneity were associated with walking for transport among middle-age residents of Brisbane, Australia.