The aim of the research was to investigate the relationship during adolescence among social deviancy, either perceived or experienced, and moral cognitions, and transgressive behaviours. 468 subjects took part in the research, 272 males (mean age 17.47; sd = 1.33) and 196 females (mean age 17.64; sd = 1.08) attending the 11th and the 13th school grade. The following measures were used: a scale for evaluating the frequency of transgressive behaviours, two scales for assessing exposure to violence (both as a victim and as a witness), a scale for measuring perception of illegality in the neighbourhood, two scales for assessing the seriousness of deviant behaviours and one for evaluating moral disengagement. The relationship among variables was investigated through a structural equations’ model. We tested the hypothesis that social deviancy, either perceived or experienced, should directly act upon transgressive behaviour, and, indirectly, through the mediation of moral cognitions. Result showed the plausibility of the hypothesized model, both in males and in females. Moral cognitions appeared to have a strong influence upon transgressive behaviour but they are, in turn, influenced by social deviancy. The latter exerts also a direct influence upon transgressive behaviour in adolescence. Results and implications for intervention are discussed.