The goal of this study was to assess the effects of a school-based smoking prevention programme that used both a video and peer-led discussion groups among Romanian junior high school students aged 13–14 years. The programme embraced the social influence approach and concentrated on enhancing self-efficacy and the acquisition of cigarette refusal skills. Twenty schools were randomly assigned to the control and experimental conditions, resulting in 55 participating classes from the seventh grade (28 in the control group and 27 in the experimental group). Pretest and 9 months follow-up data on weekly smoking initiation and psychosocial variables were collected from 1071 students. Multilevel logistic regression analyses demonstrated a significant effect of the programme on adolescents' smoking behaviour after 9 months. At post-test, weekly smoking onset was 4.5% in the experimental group versus 9.5% in the control group. Furthermore, the programme had significant effects on smoking-related beliefs. In the experimental group, this resulted in a more negative attitude towards smoking, increased social self-efficacy levels and a more negative intention towards smoking. These findings show that short-term effects of the smoking prevention programme can be realized in Romania. More studies are needed to analyse how to maintain these effects over time.