Posttraumatic stress disorder (PTSD) is an anxiety condition that often arises following a traumatic experience. It has commonly been argued that impaired consciousness associated with mild brain injury (MBI) precludes encoding of the traumatic experience, and this prevents PTSD development. This review considers the available evidence on PTSD following MBI and indicates the distinctive nature of PTSD after MBI. The review then discusses the possible mechanisms that may mediate PTSD in this population. The interaction of PTSD and postconcussive symptoms is discussed within a cognitive model that emphasizes the role of catastrophic interpretations of postconcussive symptoms. Finally, the implications of PTSD after MBI for assessment and treatment are reviewed.