The catastrophic events of September 11, 2001, significantly raised this country's interest in and concern about the psychological consequences of mass trauma and for good reason. Epidemiological studies conducted 1 to 2 months after 9/11 reported prevalence rates of posttraumatic stress disorder (PTSD) in Lower Manhattan of between 7–11% (Galea et al., 2002; Schlenger et al., 2002), a much higher figure than the 4% or less in the rest of the country (Schlenger et al., 2002). Other studies documented an increase in stress-related symptoms across the entire country in the immediate days and weeks after 9/11, although the prevalence of PTSD decreased substantially with distance from ground zero (Silver et al., 2002; Blanchard et al., 2004). In addition, there was a small, but statistically significant increase in the use of psychiatric medications among people living in Manhattan in the month following the attacks on the World Trade Center (Boscarino et al., 2003) and a substantial proportion (29%) of Manhattanites increased their use of alcohol, cigarettes, and marijuana 5–8 weeks later (Vlahov et al., 2002). Individuals who increased their substance use were more likely to experience PTSD and depression (Vlahov et al., 2002). These studies serve to illustrate the significant psychological impact even a single incident of terrorism can have and the need to have appropriate resources available to assist those who develop significant psychological difficulties in the aftermath of such an event.

There has been substantial progress over the last 15 years in the development and validation of effective psychological treatments for PTSD.