Many brain injuries are caused by traumatic events, such as high-speed motor vehicle accidents, assaults, and military combat engagement. These events also commonly precipitate acute anxiety and stress reactions, including posttraumatic stress disorder (PTSD). The association between traumatic brain injury (TBI) and PTSD has received increased recent attention in the context of U.S. military injuries in Iraq and Afghanistan. Because of the high prevalence of exposure to explosive munitions, TBI has been labeled a "signature injury" of the war in Iraq (Keltner and Cooke 2007; Okie 2005). A large proportion of these TBIs are mild. A question that is receiving considerable attention is the nature of the interaction between PTSD and mild TBI (mTBI). It has become increasingly apparent that the combination of postdeployment PTSD and history of deployment-related mTBI is an extremely common and important, but poorly understood, phenomenon associated with current military conflict. Considerable attention and ongoing research investigations are focused in this area.