Systemic therapy is a frequently used form of psychotherapy for the treatment of mental disorders in children and adolescents. The present study reports the results of the first meta-analysis on the effects of systemic treatment of mental disorders and behavior problems in children and adolescents. Based on systematic search in electronic databases (PsycINFO, Psyndex, PubMed, ISI Web of Knowledge, CINAHL),k = 56 randomized, controlled trials met the inclusion criteria. We computed a random-effects meta-analysis. Systemic therapy showed small-to-medium effects in comparison with an untreated control group (posttest:k = 7,g = .59 standard deviation units, follow-up:k = 2,g = .27) and alternative treatment (posttest:k = 43,g = .32, follow-up:k = 38,g = .28). At follow-up, longer interventions produced larger effect sizes. No other moderator effects were identified. Although available randomized, controlled trials show convincing results, their effects refer to a limited number of systemic approaches and mental disorders, and also pertain to adolescents rather than younger children. Thus, more research is needed before more general conclusions about the effects of systemic therapy can be drawn. [ABSTRACT FROM PUBLISHER]