This study aims to find out the determinant factors affecting fruit consumption behaviour in Portuguese young people, based on the Health Action Process Approach (HAPA) model, and determine if this model explains differences according to gender, age and rural/urban environments. This research is innovative because it tests the HAPA model with young people, and because it adds social support to the HAPA model as an extra predictor of young people's behaviour. To gather the data, a questionnaire survey was applied in two public schools, one in a rural area and the other in a city. The survey was answered by 266 Portuguese young people, aged 15–21 years, from the 10th to the 12th grades. Authorization for the survey was given in advance, from the Ministry of Education, schools and parents, after which the survey was performed. Before applying the questionnaire, two pre‐tests were carried out, each with ten participants and with similar characteristics to the population studied. This study analyses action self‐efficacy, outcome expectancies, action planning, risk perception, intention, maintenance self‐efficacy and social support variables. The result was obtained through a two‐step process, by determining the measurement and structural model, using Smart PLS 2.0. The results show that young females have more factors determining fruit consumption, with greater social support for action self‐efficacy, greater maintenance self‐efficacy through action self‐efficacy, and greater perception of risk regarding fruit consumption. In terms of age, young people over 16 years present greater outcome expectations for the intention, greater perception of risk and action self‐efficacy for fruit consumption. The multi‐group analysis referring to differences between young people living in rural or urban environments did not show proof of the model giving a better explanation of one situation or the other. It can be concluded that the HAPA model is appropriate to the investigation of behaviour factors that influence young people's fruit consumption. The results also indicate that in the scope of the behaviour analysed the proposed model gives a better explanation for females and for those over 16 years.