At present, the identification of psychological factors as a determinant of the illegal behaviour of adolescents is of great importance. The mental model allows explaining and predicting the behaviour of other people and reflecting one’s own mental inner reality. The study of the mental model in adolescents with delinquent and law-abiding behaviour using specially designed narratives provided us with the opportunity to analyse the understanding by adolescents, who have committed and not committed crimes, of the mental states of their own and that of another person, as well as the causes of such states in the process of social interactions. The ability to understand the mental world is paramount and necessary for understanding social interactions, for the correct formation of motives and semantic attitudes of the individual. The results of an empirical study allowed us to confirm the hypothesis that the deficit of the mental model is formed in the family; it is associated with the personality characteristics of the adolescent and, obviously, affects the formation of delinquent behaviour.