Posttraumatic stress disorder (PTSD) is one of the most common but misunderstood psychiatric disorders. The lifetime prevalence of PTSD is generally estimated to be in the 7% to 9% range,1 which indicates that the disorder is indeed a common one. However, comorbidity of PTSD appears to be more the rule than the exception, with the highest rates found in people with major depression,2 severe mental illness,3 and substance use disorders.4 The high comorbidity of PTSD with other disorders, and the fact that it only rarely occurs without comorbidities, has led to considerable confusion in both diagnosing PTSD and in distinguishing its effects from those of the disorders with which it so often co-occurs.