Following the attacks in the Île-de-France region from January 7 to 9, 2015, Santé publique France and the Île-de-France Regional Health Agency (ARS) launched the IMPACTS epidemiological survey. The objective is to assess, among those exposed to these attacks, the psychological and traumatic impact and its predictive factors, as well as the use of healthcare services. The study took place from June to October 2015. The study population was defined as civilians exposed to the attacks as well as responders involved in the response, according to Criterion A of the DSM-5 PTSD. Questionnaires were administered by psychologists trained in psychological trauma to 190 civilians and 232 responders (law enforcement and emergency services, medical-psychological support, and nonprofit organizations). Among the civilian population, 18% had PTSD and 20% had depressive and anxiety disorders (in the absence of PTSD). One-quarter of the individuals had consulted a doctor for a health problem other than a psychological one that they considered related to the events. One-third of the civilians found themselves unable to work. More than half of the exposed individuals received medical-psychological care or support in the aftermath of the events. Factors associated with PTSD at 6 months include the STRS score (Shortness of breath, Tremulousness, Racing heart, and Sweating rating scale) and low social support. Factors that increase the likelihood of developing depressive or anxiety disorders (in the absence of PTSD) include being female, a low socioeconomic status, an economic impact on the company where the person works, and the lack of immediate care from emergency medical and psychological services. Among first responders, 3% developed PTSD and 14% developed at least one anxiety disorder. Half of them received care in the aftermath of the attacks. This study highlighted the importance of medical and psychological care, the identification of all victims (those directly threatened or witnesses), as well as the need to raise awareness among healthcare professionals (both hospital-based and private practitioners) regarding the issue of psychotrauma to ensure effective care coordination. Among first responders, a lack of preparation and training for stress appears to have been a risk factor for PTSD.