Obesity is one of today’s top public health concerns and its prevalence has increased dramatically over the last two decades. In the late 1970’s, 12.7% of men and 17% of women were medically obese. By 2000 these proportions had risen to 27.7% and 34% respectively. Large spatial differences in the incidence of obesity have led many to claim that variations in the built environment, by affecting exercise and diet, may have a large impact on obesity. Compact neighborhoods may induce people to use their cars less often than those where buildings are scattered. However, before we rush to redesign neighborhoods, it is important to note that a positive correlation between sprawl and obesity does not necessarily imply that sprawl causes obesity or that reducing sprawl will lead people to lose weight.