The effects of Home-Start compared to Home-Start extended with Triple P group training were studied. The underlying theoretical models of change of both programs complement each other and therefore it was assumed that combined support leads to increased positive outcomes. Outcomes related to parental wellbeing, parenting behaviour and child behaviour were included. One hundred forty four parents, all mothers, were randomly assigned to either the Home-Start program or the combined support of Home-Start and Triple P group level 4. Parents reported on wellbeing, parenting behaviour, and child behaviour at baseline, post-program and at 6-month follow-up. Based on intention to treat analyses, families in the combined intervention condition showed similar effects on the majority of primary and secondary outcomes as the only receiving Home-Start condition. A negative effect on parental depression and on two subscales of the Child Behavioral Checklist (anxiety and oppositional defiant behaviour) was found for families in the combined Home Start and Triple-P condition. The hypothesized stronger positive effect of combining Home-Start and Triple P support on selected outcome measures was not confirmed. Combining promising evidence-based parenting programs with complementary underlying theoretical frameworks does not necessarily lead to better results.