To elucidate the role of neighborhood walkability and crime on weight loss, we examined data from older adults residing in Chicago who participated in a randomized controlled trial lifestyle intervention. Controlling for individual demographic characteristics and the intervention assignment, the neighborhood homicide rate was significantly associated with weight change. Participants who resided in neighborhoods above the 50th percentile of homicide rate actually gained weight between pre- and post-intervention. On the other hand, there was no significant relationship between the level of walkability and weight loss. Our findings suggest that the social environment related to neighborhood crime may play a more important role in weight loss than the built environment, such as walkability. Urban characteristics related to walkability, such as sidewalks, may increase physical activity, however, interventions aiming to increase physical activity to promote weight loss will benefit by addressing the neighborhood social environment that determines how people navigate space.