This is a prospective, longitudinal cohort study to evaluate the associations between indices of brain structure and function (measured at baseline, as soon as possible after injury) and course of post-traumatic stress disorder (PTSD) symptoms. Subjects will be service members who have sustained mild traumatic brain injury (classified as either "impact-induced mTBI" or "blast-induced mTBI"; n = 100 completers) or an extracranial injury (ECI) with no evidence of traumatic brain injury (TBI) (n = 100 completers). Subjects will complete an assessment battery at baseline and 6 months later that includes (1) structural magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) derived from a 3-Tesla magnet; (2) event-related brain potentials (ERPs) derived from brain electrical activity; (3) neurocognitive tests; and (4) neurological soft signs (NSS). Specific indices of brain structure and function derived from these assessments are hypothesized to demonstrate a significant relationship with course of PTSD symptoms, which will be measured at baseline, 3 months, and 6 months.

Inclusion Criteria:

1. Injured while deployed or stateside
2. Must be diagnosed TBI positive or certified as TBI negative by a licensed medical practitioner using Department of Defense (DoD) criteria
3. For mTBI subjects, an initial score of 13-15 on the Glasgow Coma Scale
4. Aged 18-50
5. Defense Enrollment Eligibility Reporting System (DEERS) eligible

Exclusion Criteria:

1. Unable or unwilling to provide informed consent and Health Insurance Portability and Accountability Act (HIPAA) authorization ("unable" includes cases in which the potential subject cannot read and understand English well enough to provide informed consent)
2. Penetrating head injury
3. Medical chart reveals a history of significant neurological condition(s) (reviewed on a case by case basis)
4. Diagnosis with or undergoing treatment for an illness that could affect brain function (reviewed on a case-by-case basis)
5. History of major psychiatric condition(s) that interfere with daily functioning as revealed in the medical chart or by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID)
6. Record of drug or alcohol abuse or dependence in the past six months as documented in medical history review
7. Medical chart or SCID reveals current or lifetime PTSD diagnosis related to non-combat life events that occurred prior to most recent deployment

Service members who have sustained mild TBI or extracranial injury (ECI), and have received care at Walter Reed National Military Medical Center or Fort Belvoir Community Hospital.