Eight to 11 months after the November 2015 attacks, Santé publique France launched a post-attack public health survey between July 7 and November 10, 2016. This web-based questionnaire survey, conducted on a voluntary basis, targeted the population whose exposures met criterion A for post-traumatic stress disorder (PTSD) as defined in the DSM-5 (exposure to death or serious injury). Its objectives were to estimate the psychological impact and to better understand the use of healthcare services and the factors associated with this use. This article presents the initial results concerning members of the civilian population (excluding emergency responders and healthcare personnel) who participated in this survey. The target population was informed about the study through the media, victims’ associations, victim support organizations, volunteer medical liaisons, as well as through visits to cafés and to residents living near the attack sites. Volunteers were asked to complete an inclusion questionnaire on the Santé publique France website, after which they were directed to an epidemiological questionnaire. This questionnaire gathered information on their sociodemographic characteristics, psychological history, exposure to the attacks and their consequences, and their mental health—including the PTSD Checklist for DSM-5 (PCL-5), Hospital Anxiety and Depression Scale (HAD), Prigerson’s Inventory of Complicated Grief (ICG)—and their use of medical and psychological care services. The impact was significant, with probable post-traumatic stress disorder (PTSD) found in 54% of those directly threatened (directly targeted, injured), 27% of on-site witnesses, and 21% of nearby witnesses. For those in mourning (i.e., individuals who had lost someone they considered close) without other exposure, the prevalence of probable PTSD was 54%. Possible complicated grief (a score above 25 on the Prigerson questionnaire) was observed in 66% of these bereaved individuals. Among those with probable PTSD, 46% reported not having undergone regular treatment with a psychologist or physician. This proportion was higher among on-site and nearby witnesses (63%) and among bereaved individuals not directly exposed (46%) than among those directly threatened (33%). These initial findings suggest a need to strengthen and expand access to care in the medium term.