Following the series of terrorist attacks that took place in the Île-de-France region from January 7 to 9, 2015, Santé publique France and the Île-de-France Regional Health Agency (ARS) conducted the IMPACTS epidemiological survey. The objective was to assess the psychotraumatic impact of these attacks on those exposed to them and on those involved in caring for the victims and restoring public order. The study also sought to determine whether these individuals sought medical care following these events. The study was conducted in two phases, 6 and 18 months after the events. Two population groups were studied. The first group consisted of members of the civilian population who had been exposed to the attacks according to Criterion A for post-traumatic stress disorder (PTSD) in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5). The second group consisted of responders involved in the response to the attacks. Thus, psychologists trained in psychological trauma interviewed 190 civilians and 232 responders (law enforcement and emergency personnel, medical and psychological support staff, firefighters, and nonprofit personnel) to gather their experiences using questionnaires. The results show that, among the civilian population, 18% of individuals had PTSD, 20% had depressive or anxiety disorders without PTSD, and 25% had consulted a doctor for a somatic health problem they considered to be related to the events. More than half of those exposed received medical-psychological care or psychological support following the events. Among first responders, 3% exhibited PTSD and at least 14% had an anxiety disorder. Half of them received psychological support following the attacks. This study highlighted the importance of identifying all potential victims of terrorist attacks (those directly threatened or witnesses) and offering them potential medical-psychological care. It also underscored the need to raise awareness among healthcare professionals regarding the consequences of psychological trauma so that they can provide effective therapeutic support.