The use of custodial sentences to prevent youth crime in Canada has been part of the Canadian juvenile justice system since the enactment of the Youth Offenders Act (YOA) in 1984. In recent years, Federal attempts have been made to change the YOA to lessen the possibility that sentencing judges will order custody. Since 1995, the desirability of alternatives to custody has been clearly articulated in the YOA. In addition, judges contemplating custody must order a predisposition report written by a probation officer. The multisystemic therapy (MST) approach is being evaluated as a community-based option that focuses on a social-ecological approach to understanding antisocial behavior. The underlying premise of MST is that criminal conduct is multicausal; therefore, effective interventions must recognize this fact and address multiple sources of criminogenic influence. The implementation of MST in Ontario, Canada, is being evaluated using scientific methods that include random assignment, a control group, a large sample, and long-term follow-up. Outcome data for the first cohort of cases are to be reported in 1999. In support of alternatives to custody, the authors believe positive outcomes are best achieved by targeting the needs of high-risk youth, community safety is promoted by addressing the problems of youth in their natural environments, and effectiveness is best achieved using services with clear track records of positive outcomes as identified in rigorous outcome evaluations. 28 references