Objective: This study evaluated the efficacy of Entre Dos Mundos/Between Two Worlds (EDM) prevention for Latino adolescents. Method: In an experimental trial to compare implementation formats, 41 Latino families were randomly assigned to EDM action-oriented skills training groups, and 47 families were randomly assigned to unstructured EDM support groups. Both groups addressed identical EDM session themes. Results: No significant differences between the intervention delivery methods were found; both EDM groups showed improvements. Statistically significant dosage effects occurred from pretest to posttest. Controlling for pretest scores, family income, parent education, and time spent in the United States, parents who attended more group sessions reported significant decreases in their adolescent child's aggression, oppositional defiant behavior, attention deficit hyperactivity disorder, and attention problems, with concomitant gains in family adaptability, bicultural support, and bicultural identity integration. Effect sizes for high-dosage families were moderate to large. Conclusions: Initial evidence suggests that EDM is efficacious for immigrant Latino adolescents. (Contains 5 tables.)