In the current study, we aim to examine the link between exposure to multiple traumatic events (polyvictimization), posttraumatic stress disorder (PTSD) symptoms (PTSS), and psychiatric symptomatology in early adolescence. Furthermore, we aim to explore the mediating roles of defense styles and coping styles in the associations between polyvictimization, PTSS, and psychiatric symptomatology. Data from a Danish national representative sample of 390 eighth-grade students with a mean age of 13.95 (SD = 0.37) years were used. Participants responded to validated self-report questionnaires in 2001. The dimensions of immature defense styles and emotional and avoidance coping mediated the positive associations between polyvictimization, PTSS, and psychiatric symptomatology. Serial multiple mediation indicated that the sum of exposure to traumatic events was significantly associated with more immature defense styles, associated with both high levels emotional and avoidance coping, which, in turn, were associated with high levels of PTSS and psychiatric symptomatology. Polyvictimization is related to adverse outcomes in early adolescence. Both immature defense styles and emotional and avoidance coping styles should be considered as risk factors for the development of psychological distress following exposure to multiple traumas.