Adolescents are among the most frequent users of social media websites, raising concern about the dangers of cyber bullying or cybervictimization (CV). A 12-month longitudinal study examined the unique, prospective relation of CV to the development of negative self-cognitions and depressive symptoms in a community sample of 827 children and young adolescents (ages 8–13; 55.1 % female) from the southeastern United States. Over and above conventional types of peer victimization, CV significantly predicted changes in self-referential negative cognitions, victimization-related cognitive reactions, and depressive symptoms, even after controlling for baseline levels of the dependent variables. Results also showed that CV was significantly less stable than other forms of victimization and tended to increase slightly with time. The study highlights the unique effects of CV and has implications for research and practice.