The analysis assessed two major models to examine why the changes had the effects they did on crime. One is labeled the opportunity model, because access affects a potential offender's opportunity to commit crime. Others suggest that the physical environment affects crime through its effects on informal social control. They propose a second model: a community model in which the physical environment affects crime by strengthening community cohesion and social organization, which, in turn, leads to a decrease in crime. The residents of the Five Oaks neighborhood in Dayton, Ohio, organized a major effort to stabilize the neighborhood. The combination of its location near major roads, its proximity to downtown, and its grid pattern made it a permeable neighborhood. This resulted in a high volume of cut- through commuter traffic and, according to the police, was a major reason that a number of drug houses were established in the neighborhood. Drug buyers could drive into the neighborhood, make their buys, and get away from the neighborhood quickly. Many Five Oaks residents and city officials worked together for 1 year to develop a stabilization plan to address the problems. The stabilization plan contained several components, including a street-closing plan, coordination of community-based policing, and programs to encourage home ownership and housing maintenance. The defensible space plan originally was composed by Oscar Newman, and it was subsequently revised by residents and city planners. The plan closed 35 streets and 26 alleys. Data on a number of issues were collected for years before and after the plan was implemented, including information on crime, traffic, and the addresses of persons arrested for committing crimes in the neighborhood. Comparisons of crime data and of residents' perceptions of crime between the pre-implementation and post-implementation periods show significant improvements. The data provide greater support for the opportunity model of community crime prevention than for the community model. Cautions are provided regarding transplanting the same plan elsewhere. 6 tables and 29 references