Multisystemic treatment (MST) is a family- and home-based therapeutic approach that has been found to be effective in treating antisocial youths and that has recently been applied to youths with serious emotional disturbances. In light of the increasing dissemination of MST, this review examines the effectiveness of MST by quantifying and summarizing the magnitude of effects (treatment outcomes) across all eligible MST outcome studies. Included in a meta-analysis were 7 primary outcome studies and 4 secondary studies involving a total of708 participants. Results indicated that across different presenting problems and samples, the average effect of MST was d = .55; following treatment, youths and their families treated with MST were functioning better than 70% of youths and families treated alternatively. Results also showed that the average effect of MST was larger in studies involving graduate student therapists (i.e., efficacy studies; d = .81) than in studies with therapists from the community (i.e., effectiveness studies; d = .26). In addition, MST demonstrated larger effects on measures of family relations than on measures of individual adjustment or peer relations.