This report describes 1) the evaluation of the Familias Fuertes primary prevention program in three countries (Bolivia, Colombia, and Ecuador) and 2) the effect of program participation on parenting practices. Familias Fuertes was implemented in Bolivia (10 groups, 96 parents), Colombia (12 groups, 173 parents), and Ecuador (five groups, 42 parents) to prevent the initiation and reduce the prevalence of health-compromising behaviors among adolescents by strengthening family relationships and enhancing parenting skills. The program consists of seven group sessions (for 6–12 families) designed for parents/caregivers and their 10–14-year-old child. Parents/caregivers answered a survey before the first session and at the completion of the program. The survey measured two important mediating constructs: "positive parenting" and "parental hostility." The Pan American Health Organization provided training for facilitators. After the program, parents/caregivers from all three countries reported significantly higher mean scores for "positive parenting" and significantly lower mean scores for "parental hostility" than at the pre-test. "Positive parenting" practices paired with low "parental hostility" are fundamental to strengthening the relationship between parents/caregivers and the children and reducing adolescents' health-compromising behaviors. More research is needed to examine the long-term impact of the program on adolescent behaviors.