Background Intensive care units (ICU) are among the healthcare services most affected by the COVID-19 crisis. Stressors related to insecurity, unpredictability, patient death and family distress are significant, and put healthcare workers (HCWs) at high risk of post-traumatic stress disorder (PTSD). The aims of this study were to measure the prevalence of post-traumatic stress disorder in HCWs and to identify risk factors and protective factors during the epidemic in France. Methods During the first peak of the epidemic (from 22 April to 13 May 2020), we assessed sources of stress (PS-ICU scale), mental health (GHQ-12) and coping strategies (Brief-COPE). Three months later (03 June to 6 July 2020), PTSD was assessed using the IES-R scale, with additional questions about sources of support. Data were collected using self-report questionnaires administered online. Results Among 2153 professionals who participated in the study, 20.6% suffered from potential PTSD, mostly intrusion symptoms. Risk factors for the development of PTSD were having experienced additional difficult events during the crisis, having a high level of psychological distress, a high level of perceived stress related to the workload and human resources issues, the emotional burden related to the patient and family, and stressors specific to COVID-19 during the first peak of the crisis. The use of positive thinking coping strategies decreased the relationship between perceived stress and the presence of PTSD, while social support seeking strategies increased the relationship. Finally, the HCWs preferred to use support from colleagues, relatives and/or a psychologist, and very few used the telephone hotlines. Conclusion The epidemic has had a strong traumatic impact on intensive care HCWs. Given the risk of PTSD, we need to consider implementing easily-accessible support services that focus on positive thinking coping strategies, during and after the crisis.