This paper examines the use of a behavioral-ecological model to diagnose and prescribe interventions for a community problem. The paper is presented as a case study of a community-based organization that used the model in the treatment and prevention of Chicano gang delinquency. Other purposes of this work included a replication and extension of similar work performed in a different environment and with different subjects as well as a test of the generality of behavioral methods to the treatment and prevention of Chicano gang delinquency. In general, all three purposes were accomplished. Some unanticipated outcomes and future directions are discussed.Although gang delinquency as a social problem has been extensively studied and the focus of a number of intervention efforts, the use of a behavioral-ecological model to diagnose and prescribe interventions appropriate to this problem has not often been reported. Moreover, little work of any kind has been reported on natural environment interventions tested specifically with Chicano gang delinquents. In view of the successful application of behavior modication to many delinquent behaviors (Braukmann,