Efficacy of a smoking prevention programme in Catalan secondary schools: A cluster-randomized controlled trial in Spain ; Aims: To evaluate the efficacy of a school-based educational programme in reducing the incidence and prevalence of smoking in secondary school students (compulsory secondary education: CSE) in Catalonia (Spain). Design: Cluster-randomized controlled trial. Setting: Schools in the Tarragona Health Care Region of Spain. Participants: All students enrolled in the first year of CSE during the 2007-08 school year in the 29 participating schools (n=2245); 1583 students completed the follow-up over the 4-year study period (804 and 779 in the control and intervention groups, respectively). Measures: Self-reported questionnaires were administered during the first quarter of the 2007, 2008, 2009 and 2010 school years. A smoker was defined as 'smoking cigarettes daily or occasionally within the past 30days'. Multi-level logistic regression analysis was conducted to analyse the prevalence and incidence of smoking between the intervention and control groups. Intervention: A school-based educational programme comprising seven modules, each with a different approach to smoking habits. Each module included activities, work-shops and/or class sessions. Findings: The initial prevalence of smokers in the control and intervention groups who completed the follow-up was 3.9% and 4.2%, respectively. At the end of the study, the prevalence of smokers was 24.4% in the control group and 19.9% in the intervention group. The accumulated incidence of new smokers was 230.57/1000 in the control group and 183.65/1000 in the intervention group. The adjusted odds ratio (OR) comparing the intervention group with the control group was 0.75 [95% confidence interval (CI)=0.49, 1.15] for smoking prevalence, and 0.74 (95% CI=0.48, 1.14) for smoking incidence. Conclusions: A school-based educational interventi