Summary The high prevalence of post-traumatic stress disorders (PTSDs) in the workplace is an irrefutable fact. The statistics of the Commission de la santé et de la sécurité du travail (CSST) for the 2002 to 2004 period indicate that payouts totalling $17,747,600 went to workers with PTSDs, which is considerably more than payouts related to stress and anxiety ($7,724,669), depressive conditions ($3,626,814), and occupational burnout ($797,165). PTSDs also have repercussions for the psychosocial functioning, return to work, and quality of life of the individuals affected. Yet despite these consequences, few studies have evaluated the effectiveness of interventions designed to prevent PTSDs and the results of these interventions remain inconclusive. Given the mission pursued by the Centre jeunesse de Montréal – Institut universitaire (CJM-IU, or Montreal youth centre, University institute), which is to assist and protect its clients in difficulty, its personnel has a high potential of exposure to traumatic events. For this reason, in 1999 the CJM-IU developed an intervention, including a post-traumatic intervention (PTI) protocol and associated management measures, to prevent and attenuate the development of post-traumatic reactions, acute stress conditions, and post-traumatic stress disorders in workers who have experienced such events. Aware of the importance of developing effective interventions, the CJM-IU embarked on a process of scientifically evaluating such interventions. The general objective of the research activity was to document the services offered to workers who have faced potentially traumatic events and to evaluate the effectiveness of the CJM-IU intervention. Phase I, which is the subject of this report, was dedicated to describing the CJM-IU intervention in an actual application context, identifying the underlying theory, and documenting alternative interventions carried out in other Québec youth centres. Phase II will aim to evaluate the intervention’s impact on workers who have faced traumatic events and will be the focus of a subsequent project.Phase I was exploratory and descriptive in nature. In-depth case studies were conducted on the basis of interviews of the intervention developers, members of the post-traumatic intervention team (PTIT), the external consultant for the PTIT, the senior executive responsible for the team, and the managers who sat on the coordination committees. Relevant documents and scientific literature were also examined. The first-level managers and the workers at risk of exposure to traumatic events participated in this project by completing a questionnaire. Lastly, an inventory was taken of alternative interventions designed to prevent PTSDs in personnel at Québec’s other youth centres by means of a survey conducted of the human resources departments of the various establishments. The qualitative data analysis was supported by the Vivo9 software program, while the quantitative data analyses were descriptive in nature and carried out using the SPSS software program. The PTI model was validated with the designers and underwent logic analysis. This analysis showed the theoretical and empirical relevance of the CJM-IU intervention, which incorporates the main scientific data available on the prevention of both secondary and tertiary post-traumatic reactions. The CJM-IU’s immediate and “post-immediate” interventions are based on recommendations made by official American and British organizations working in the mental health field. Documents on the application of the PTI allowed us to ascertain whether overall there was a high level of compliance with the theoretical model. The meetings held by the PTIT members adhered to the planned intervention framework. The recommended intervention strategies were used by the PTIT members and adapted to the particular needs of the personnel affected. However, a few deficiencies were noted in the application of some cognitive and behavioural strategies, such as diaphragmatic breathing, Socratic questioning, and stress inoculation. These results suggest the need for ongoing continuing education efforts and supervision of the PTIT members in their activities. Moreover, further thought is needed about the amount of leave time given to members of the PTIT team. We observed a degree of pressure exerted partly by professional duties and partly by the limited availability of the team members to do their own training activities or simply to carry out their intervention. In the longer term, once the two phases have been completed, the researchers will have more conclusive data for making recommendations to Québec’s youth centres and other organizations that have workers at high risk of exposure to traumatic events and that wish to implement effective programs for managing and preventing PTSD-related disabilities.