It has long been recognized that traumatic events can produce psychiatric symptoms (1) in individuals who were previously well adjusted; however, the overriding notion was that the stress-induced symptoms were transient (Wilson, 1994). The Diagnostic and Statistical Manual for Mental Disorders (DSM; American Psychiatric Association, 1952) contained the diagnosis of "gross stress reaction" and DSM-II (APA, 1968) contained the diagnosis of "transient situational disturbance." As the DSM-II diagnostic label indicates, both versions assumed that trauma- induced symptom-responses were temporary and would dissipate, and any symptoms that remained were characteristic of a separate psychological disturbance (McNally, 1999). The return of Vietnam veterans and increasing awareness of their symptoms generated a debate that helped change the professional perception of psychological response to traumatic events (McNally, 1999). The APA DSM-III Task Force explored cases of individuals who had experienced incidents of war, rape, and natural disasters. They concluded that these types of events could give rise to a common constellation of symptoms and a unique psychological syndrome. Based on their recommendation, DSM-III (APA, 1980) was the first edition to include the diagnostic label of Posttraumatic Stress Disorder (PTSD). The diagnosis has remained throughout the revisions of DSM-III-R (APA, 1987), DSM-IV (APA, 1994), and DSM-IV-TR (APA, 2000) with slight modifications to the original defined criteria. The current criteria include symptoms from three defined symptom clusters: (1) recurrent re-experiencing of the trauma (e.g., nightmares, intrusive thoughts), (2) avoidance symptoms (e.g., avoidance of the reminders of the trauma, avoidance of thoughts about the trauma, emotional numbing), and (3) increased arousal (e.g., heightened startle response, insomnia). The diagnosis of PTSD is satisfied if the symptoms persist for a minimum of 4 weeks. Exposure to the types of traumatic events that can lead to psychiatric difficulties is extremely common. Nearly 60% of men and 50% of women experience a traumatic event at some point during their lifetime (Resick, 2001; Schnurr, Friedman, & Bernardy, 2002). There is great variation in the prevalence rates of PTSD in the general population. Kessler, Sonnega, Bromet, Hughes, and Nelson (1995) found that among the general population, estimates of lifetime PTSD are 5% for men and 10% for women. Among traumatized individuals, lifetime prevalence rates increase to 8% in men and 20% in women (Kessler et al.). It is difficult to gather a very clear picture of the frequency of this disorder by looking at the general population because the likelihood of developing PTSD varies with the type of trauma experienced. Those that occur with the most frequency (motor vehicle accident, witnessing someone being injured/killed, and natural disasters) tend to have lower PTSD prevalence rates than those less frequently experienced (combat, child abuse, and sexual .assault), with sexual assault being the most likely event to result in PTSD (Resick). Kessler and colleagues found that the vast majority of men (88%) and women (79%) who met criteria for PTSD also met criteria for at least one other DSM diagnosis. Substance abuse and depression are the most frequent, with co-morbidity rates consistently exceeding 50% (Gold, 2004; Kessler et al.; McFarlane & de Girolamo, 1996; Resick).