MST is an intensive home-based service for high risk youth that has been developed and evaluated in the United States and intensively studied since 1997 in four Ontario communities. MST adopts a social-ecological approach to understanding anti-social behavior, and the underlying premise of MST is that criminal conduct is multi-causal. An evaluation was conducted of 147 cases in Ontario involving MST that focused on referral profile and post-treatment recidivism. Interim results suggested MST was effective in changing family functioning. Specifically, after 6 months, 28 percent of the control group had been convicted of a new offense compared to 21 percent of the MST group. In addition, preliminary analysis of costs associated with short-term outcomes related to MST intervention suggested usual service outcomes were considerably more costly. The findings are discussed in terms of the potential of an ATC program to influence service providers and policy-makers in the Canadian juvenile justice system. Future findings with respect to MST implementation and research implications of the Ontario clinical trial are also examined. 18 references, 3 tables, and 1 figure