The aim of this randomized controlled trial was to evaluate the efficacy of an evidence-based parenting program (the Triple P-Positive Parenting Program), intending to improve parenting skills and children’s well-being. Parents participating in a Group Triple P program (n = 50 couples) were compared to parents of a non-treated control group (n = 50 couples) and parents participating in a marital distress prevention program (Couples Coping Enhancement Training: CCET) (n = 50 couples). The two major goals of this study were: (a) to evaluate the efficacy of Triple P compared to the two other treatment conditions over a time-span of one year and (b) to answer the question whether this program that was developed in Australia is culturally accepted by Swiss parents. Results revealed that Triple P was effective with Swiss families. Mothers of the Triple P group showed significant improvements in parenting, parenting self-esteem, and a decrease in stressors related to parenting. Women trained in Triple P also reported significantly lower rates of child’s misbehavior than women of the two other conditions. However, in men only a few significant results were found. Positive effects of the relationship training (CCET) were somewhat lower than those for the Triple P. These findings are further discussed.