The present study investigated the longitudinal association between the development of bullying (traditional bullying and cyberbullying) and the development of moral deficiencies (moral disengagement, low moral responsibility, and weak feelings of remorse) during adolescence. A total of 960 Swiss adolescents completed an electronic questionnaire in schools four times, with 6-month intervals. Results of a parallel process model showed that the initial levels of moral deficiencies were positively associated with initial scores of bullying. Furthermore, the initial levels of moral deficiencies were positively associated with the development of bullying (i.e., initial trend and changes in trend across time). In contrast, the initial level of bullying was not found to be associated with the development (i.e., the slope) of moral deficiencies. Accordingly, we conclude that moral deficiencies might be a trait that predicts the development of bullying and not vice versa. Implications of the findings for bullying prevention are discussed.