The lifetime prevalence of being exposed to a traumatic event is close to 90% for the general population, which means that it concerns almost everyone. In North America, an estimated 20-50% of those exposed to a traumatic event will have Acute Stress Disorder (ASD). Most people with ASD (around 70%) will recover without any special help in the next month. After 1 month of symptoms, we begin to talk about post-traumatic stress disorder. The most recent Canadian epidemiological study (Van Ameringen, Mancini, Patterson and Boyle, 2008) estimates the prevalence of post-traumatic stress disorder at 9.2%. On the other hand, women are significantly more at risk than men for developing Post Traumatic Stress Disorder, the prevalence can be double for women, even controlling for the type of event. Finally, when comparing different types of traumatic events, the type most likely to lead to post-traumatic stress disorder are serious sexual violence for women and military experience or exposure to a crime scene for men.