A significant proportion of people who are exposed to traumatic events suffer from post-traumatic sequelae, such as post-traumatic stress disorder (PTSD). Indicated preventive interventions soon after trauma could be appropriate. Yet, there is limited evidence for the efficacy of such interventions. Moreover, no evidence-based preventive interventions are readily available for victims in the aftermath of crises and disasters in Norway. Condensed Internet-delivered Prolonged Exposure (CIPE) is a preventive intervention designed for victims with symptoms of PTSD (PTSS) approximately one month after a traumatic event. The treatment is an internet-delivered, therapist assisted intervention, based on principles from Prolonged Exposure. CIPE has proven to be feasible, safe, and effective in previous studies. This study aims to test the effectiveness and cost-effectiveness of CIPE in the context of psychosocial crisis services in Norwegian municipalities. Hypotheses Effectiveness H1 Participants receiving CIPE + treatment as usual (TAU) will have significantly less PTSS than participants receiving TAU at 6 weeks post T1, and at 6-, and 12- months after the traumatic incident. H2 Significantly fewer participants receiving CIPE+TAU will fulfill the criteria for PTSD compared to participants receiving TAU, at 6- and 12-months post trauma. H3 Participants receiving CIPE+TAU will have significantly less symptoms of depression and insomnia than participants receiving TAU at 6 weeks post T1, and at 6-, and 12- months after the traumatic incident. H4 Participants in the CIPE+TAU-condition will report significantly higher treatment satisfaction at post-treatment, compared to those in the TAU-condition. H5 Participants with traumatic loss receiving CIPE+TAU will have significantly less symptoms of prolonged grief than such participants receiving TAU 12 months after the loss. Cost-effectiveness H6 Fewer participants in the CIPE+TAU-condition will be referred to second-tier specialty mental health services, and more will achieve improved quality of life within the first year after the traumatic incident, compared to participants in the TAU-condition. H7 The CIPE+TAU implementation is more cost-effective compared to the TAU in the short run and may even dominate TAU in the long run (i.e., more effective and less costly).