Posttraumatic stress disorder (PTSD) is a psychiatric disorder that affects 7-8% of the general U.S. population at some point during their lifetime; however, the prevalence is much higher among certain subgroups, including active duty military personnel and veterans. In this article, we review the empirical literature on the epidemiology and screening of PTSD in military and veteran populations, including the availability of sensitive and reliable screening tools. Although estimates vary across studies, evidence suggests that the prevalence of PTSD in deployed U.S. military personnel may be as high as 14-16%. Prior studies have identified trauma characteristics and pre- and posttrauma factors that increase risk of PTSD among veterans and military personnel. This information may help to inform prevention and screening efforts, as screening programs could be targeted to high-risk populations. Large-scale screening efforts have recently been implemented by the U.S. Departments of Defense and Veterans Affairs. Given the prevalence and potential consequences of PTSD among veterans and active duty military personnel, development and continued evaluation of effective screening methods is an important public health need.