BackgroundIn DSM 5, three disorders are related to trauma and/or maltreatment: Post-traumatic Stress Disorder (PTSD), Reactive Attachment Disorder (RAD) and Disinhibited Social Engagement Disorder (DSED) but how these disorders relate to each other and to traumatic events is unknown. ObjectiveWe examined 1. Prevalence of Potentially Traumatic Events (PTEs) and poly-victimization for youths in foster care. 2. Associations between single/multiple PTEs and PTSD, DSED, and the two symptom-clusters that constitute RAD: Failure to seek/accept comfort (RAD A), and Low social-emotional responsiveness/ emotion dysregulation (RAD B). Participants, setting and methodsFoster youth 11–17 years (N = 303) in Norway completed The Child and Adolescent Trauma Screen. Foster parents completed the RAD and DSED Assessment interview. ResultsFoster youth reported experiencing, on average, 3.44 PTEs each (range 0–15, SD 3.33), and 52.9 % reported PTSD symptoms at or above clinical cut off. The PTE sum score was associated with the latent factors PTSD (r = .66, p < 0.001), RAD cluster B symptoms (Low social-emotional responsiveness / emotion dysregulation, r = .28, p < 0.001) and DSED (r = .11, p = 0.046), but not with RAD cluster A symptoms (Failure to seek/accept comfort). ConclusionsThese findings raise new questions about the nature, mechanisms and timing of development of RAD and DSED. Maltreatment assessment needs to encompass a wide range of PTEs, and consider poly-victimization.