Background: The purpose of this study is to evaluate the effects of a German adaptation of the Strengthening Families Programme 10-14 (SFP 10-14; Familien Starken). Methods: A multi-centre randomised controlled trial comparing the German SFP version consisting of seven sessions and four booster-sessions with a minimal intervention on parenting as control condition. Outcomes comprise measures of adolescent substance use (initiation) and behaviour problems and are assessed at baseline, after programme delivery and at 6- and 18-month followups. Primary outcomes were lifetime tobacco, alcohol and cannabis use at 18 months. Data of n = 292 families were analysed using baseline adjusted logistic regressions and mixed models. Results: We observed reduced rates of lifetime tobacco use in analyses with follow-up respondents, but not in data using the complete intention to treat sample with multiple imputation estimates for missing data. Parents reported fewer adolescent behaviour problems in analyses with the total sample and multiple imputed data, but not in data with follow-up respondents only. There were no other significant effects of SFP 10-14. Conclusion: Overall the medium size effects found in previous US trials could not be replicated in a German context.