It has been widely assumed that patients who sustain mild traumatic brain injury (MTBI) or post-concussive syndrome develop post-traumatic stress disorder (PTSD) in response to their cognitive difficulties, diminished coping skills, or other losses. This study examined 70 patients who had previously been diagnosed as having either PTSD or MTBI. Each patient was asked to provide a highly detailed chronological history of the events which preceded, followed, and occurred during the traumatic event, to indicate whether they were rendered unconscious or had amnesia for the event, and to describe the various symptoms they developed. All (100.0%) of the PTSD patients were able to provide a highly detailed and emotionally charged recollection of the events which occurred within 15 minutes of the traumatic event in comparison to none (0.0%) of the MTBI patients. None of the MTBI patients reported symptoms such as intrusive recollections of the traumatic event, nightmares, hypervigilance, phobic or startle reactions, or became upset when they were asked to describe the traumatic event or were exposed to stimuli associated with it. These data suggest that PTSD and MTBI are two mutually exclusive disorders, and that it is highly unlikely that MTBI patients develop PTSD symptoms. Furthermore, these findings suggest that clinicians should exercise considerable caution in ruling out PTSD prior to making the diagnosis of MTBI.