Introduction:Exposure to traumatic stressful events in childhood is an important risk factor for the development of posttraumatic symptomatology. From a mentalization-based developmental perspective, childhood adversity can affect attachment in children and may result in insecure attachment and impaired mentalizing abilities, which increase the lifetime risk for psychopathology. The present cross-sectional study examined the potential mediating role of attachment insecurity and impaired mentalizing on the relationship between childhood trauma and posttraumatic symptomatology. Method: Adults who had experienced childhood neglect and abuse (n = 295, 184 patients with personality disorder and 111 community controls) completed self-report measures of posttraumatic stress disorder (PTSD) symptoms, dissociative experiences, adult attachment insecurity, and mentalizing. Results: Structural equation modelling results revealed that attachment insecurity together with lower mentalizing mediated the link between childhood trauma and PTSD symptoms, and lower mentalizing mediated the link between childhood trauma and dissociative experiences. Conclusion: The findings show that attachment insecurity and lower mentalizing play significant mediating roles in the reporting of posttraumatic symptomatology among survivors of childhood abuse and neglect, with treatment implications for mentalization-based therapy as beneficial for individuals with a history of childhood trauma.