Persistent trends in overweight and obesity have resulted in a rapid research effort focused on built environment, physical activity, and overweight. Much of the focus of this research has been on the design and form of suburbs. It suggests that several features of the suburban built environment such as low densities, poor street connectivity and the lack of sidewalks are associated with decreased physical activity and an increased risk of being overweight. But compared to suburban residents, inner city populations have higher rates of obesity and inactivity despite living in neighborhoods that are dense, have excellent street connectivity and who's streets are almost universally lined with sidewalks. We suggest that the reasons for this apparent paradox are rooted in the complex interaction of land use, infrastructure and social factors affecting inner city populations. Sometimes seemingly similar features are the result of very different processes, necessitating different policy responses to meet these challenges. For example, in suburbs, lower densities can result from government decision making that leads to restrictive zoning and land use issues. In the inner city, densities may be lowered because of abandonment and disinvestment. In the suburbs, changes in land use regulations could result in a healthier built environment. In inner cities, increasing densities will depend on reversing economic trends and investment decisions that have systematically resulted in distressed housing, abandoned buildings and vacant lots. These varying issues need to be further studied in the context of the totality of urban environments, incorporating what has been learned from other disciplines, such as economics and sociology, as well as highlighting some of the more successful inner city policy interventions, which may provide examples for communities working to improve their health. Certain disparities among urban and suburban populations in obesity and overweight, physical activity and research focus have emerged that are timely to address. Comparable research on the relationship of built environment and health is needed for urban, especially inner city, neighborhoods.