Abstract The aim of this research project is to better understand the development of post-traumatic stress disorder (PTSD) following an occupational accident by studying the risk and protection factors related to it. The project originates from a request from the policing community, where workers are frequently exposed to traumatic events (TEs). The researchers hypothesize that peri- and post-traumatic factors may better explain the development of PTSD and the adaptation to TEs experienced by exposed personnel than pre-traumatic factors. This study is original, because it is interested in the basically unstudied protection factors, distinguishes between three levels of factors (pre-, peri- and post-traumatic) and involves Québec police officers. It is a first because it includes as many men as women and consists of a retrospective component and a complementary prospective component essential to a better understanding of PTSD predictive factors. This research report mainly presents the results of the prospective component, but it makes the link with the data obtained in the retrospective research report.Eighty-three police officers from the Service de Police de la Ville de Montréal (SPVM, City of Montréal Police department) and other police forces took part, on a voluntary basis, in the prospective study with repeated measurements (quasi-experimental approach). They had all been involved in a major event between the months of May 2006 and May 2010. On average, they were evaluated between 5 and 15 days, 1 month, 3 months, and 12 months after the event. The same measuring instruments were used as during the retrospective study. Semi-structured interviews as well as self-report questionnaires were used to determine whether a PTSD was present or not, and to evaluate various predictive factors associated with the development of this disorder. The instruments were chosen for their psychometric and clinical qualities and because they allow the research hypotheses to be appropriately tested. Multivariate statistical analyses helped determine the main predictive factors in play and the strength of their impact on the modulation of PTSD.The results of the prospective study show that 3% of police officers have suffered from a clinical PTSD, while 9% have experienced a partial PTSD. However, the data from the retrospective study show that 7.6% of the police officers in the sample have suffered from a clinical PTSD, while 6.8% have experienced a partial PTSD. For the prospective component, the results of the regression analyses indicate that post-traumatic risk factors (meaning the symptoms of acute stress disorder (ASD) and depression) are the prominent predictors. Pre-traumatic risk factors (the strategy for stress management at the emotional level) and peri-traumatic risk factors (peri-traumatic distress and dissociation) are less prominent, but nevertheless remain significant risk factors. We did not observe any protection factors negatively associated with PTSD symptoms. The results of a multiple logistic regression during the retrospective study indicate that the peri-traumatic risk and protection factors (meaning dissociation and social support during the event) are the most prevalent predictors. The results of the descriptive analyses in the retrospective study show that police officers have various means and adaptation strategies for dealing with a critical event at work. The police officers mention that talking about it with their colleagues, obtaining their support, and having leisure activities are aspects that particularly help them following a TE. The police officers advise their colleagues experiencing such an event to talk about it, to consult a psychologist and, for the most part, are themselves open to the idea of receiving such a service if needed.The low PTSD rate in the police officers evaluated in this study, contrary to initial expectations, shows that police officers appear resilient, despite the fact that they represent a population at high risk of experiencing TEs in the context of their work. The results of this study confirm some current knowledge found in the literature on various populations, including police officers. Since the factors associated with PTSD development in police officers (namely dissociation, emotional and physical reactions, ASD, depressive symptoms, emotional strategies for stress management) can potentially be attenuated or prevented, specific and adapted interventions could be developed to target them better, and subsequently better prevent the development of PTSD. The factors associated with adaptation following trauma (namely stress-resistant personality, social support) can be developed or improved due to preventive strategies that will benefit from being included in police personnel training programs in general. The results of this study can enrich the training given by the Programme d'aide aux policiers et policières (PAPP, police assistance program) of the SPVM and other police forces. Also, the results confirm the importance of a preventive approach, which is already a practice favoured and applied by the PAPP. This approach could also be part of other employee assistance programs in the context of other police forces. This study, the first of this type in Québec, could serve as reference point for future studies using a sample of Québec police officers. The acquired knowledge will make it easier to identify and prevent PTSDs. Also, the formulated recommendations will enable the policing community to develop strategies likely to promote the development of protective mechanisms for future TEs as well as the reduction of existing risk factors. This study could have major spinoffs for different working groups that are also at high risk of TEs (firefighters, ambulance attendants, rescue workers, responders, etc.).