Objective: The present study aimed to evaluate the impact of a Transtheoretical Model-based programme titled ‘Fruit & Vegetable-Friendly’ on the fruit and vegetable (F&V) consumption of adolescents.Design: A quasi-experimental study. The ‘Fruit & Vegetable-Friendly’, a multicomponent intervention based on the Transtheoretical Model, was completed in eight weeks. The data were collected one week before the intervention, one week after the completion of the intervention and six months after the post-test with an F&V intake questionnaire and the stages of change, processes of change (α = 0·91), situational self-efficacy (α = 0·91) and decisional balance (α = 0·90 for pros, α = 0·87 for cons) scales. Data were analysed with the Friedman, Wilcoxon and marginal homogeneity tests.Setting: A public secondary school in Istanbul, Turkey.Participants: Seven hundred and two adolescents.Results: The mean (sd) F&V intake of adolescents in the passive stages rose from the daily average at the time of the pre-test of 3·40 (1·79) portions to 5·45 (2·54) portions on the post-test and to 5·75 (2·70) portions on the follow-up test (P < 0·01). While the students in the passive stages represented 41·6 % of the participants prior to the programme, this rate fell to 23·7 % at the post-test and to 22·7 % at the follow-up. Students in the active stages first represented 58·5 % of the participants; this rate rose to 76·4 % at the post-test and to 77·2 % at the follow-up test.Conclusions: The programme was effective in increasing the amount of F&V the adolescents consumed on a daily basis.