Universal community-oriented interventions are an important component in the prevention of youth health and behavior problems. Testing the universality of the effects of an intervention that was designed to be universal is important because it provides information about how the program operates and for whom and under what conditions it is most effective. The present study examined whether the previously established significant effects of the universal, community-based Communities That Care (CTC) prevention program on the prevalence of substance use and the variety of delinquent behaviors held equally for boys and girls and in risk-related subgroups defined by early substance use, early delinquency, and high levels of community-targeted risk at baseline. Interaction analyses of data from a panel of 4,407 students followed from Grade 5 to Grade 8 in the first randomized trial of CTC in 12 matched community pairs suggests that CTC reduced students' substance use and delinquency equally across risk-related subgroups and gender, with two exceptions: The effect of CTC on reducing substance use in 8th grade was stronger for boys than girls and the impact of CTC on reducing 8th-grade delinquency was stronger for students who were nondelinquent at baseline. (Published Abstract) 78 references