The aim of this mental health promotion initiative was to evaluate the effectiveness of a universallydelivered group behavioral family intervention (BFI) in preventing behavior problemsin children. This study investigates the transferability of an efficacious clinical programto a universal prevention intervention delivered through child and community healthservices targeting parents of preschoolers within a metropolitan health region. A quasiexperimentaltwo-group (BFI, n=804 vs. Comparison group, n=806) longitudinal designfollowed preschool aged children and their parents over a 2-year period. BFI was associatedwith significant reductions in parent- reported levels of dysfunctional parenting and parentreportedlevels of child behavior problems. Effect sizes on child behavior problems rangedfrom large (.83) to moderate (.47). Positive and significant effects were also observed in parentmental health, marital adjustment, and levels of child rearing conflict. Findings are discussedwith respect to their implication for significant population reductions in child behaviorproblems as well as the pragmatic challenges for prevention science in encouraging both theevaluation and uptake of preventive initiatives in real world settings.