Introduction :In the event of a terrorist attacks emergency psychiatrists are forced to deal with a massive influx of psychologically traumatized civilian casualties. Objective : The main objective of this study was to give guidelines on how to quickly and reliably identify the patients at risk of developing Post-Traumatic Stress Disorder (PTSD). Method : Our cohort comprised 82 subjects present inside the Bataclan (Paris, France) during the terrorist attack on November 13th 2015. The risk analysis considered all clinically relevant risk factors. All data was collected using an Internet based self-assessment questionnaire 5 to 10 months (6 months in average) after the attacks. Results : 74% of the subjects presented severe symptoms of Acute Stress Disorder (ASD). Seventeen percent were wounded by an automatic firearm. The prevalence of PTSD was 61%. We observed four significant predictive risk factors for PTSD: an elevated ASD (RR = 3.1), a low-level of trait-mindfulness (RR = 2.4), a low-level of education (RR = 1.6) and a lack of family support (RR = 1.4). Conclusion : Terrorist attacks induce an unprecedented prevalence of PTSD. For optimum emergency psychological care after a terrorist attack, severe ASD symptoms should alert the physician. Helping victims to develop their capacity to create a safe and protective environment by leveraging social resources like family, and inner resources like mindfulness could optimize global resilience.