This is a pilot trial to see if one or two 40 treatment courses of low pressure hyperbaric oxygen therapy can improve cognition and brain imaging in subjects with either chronic mild-moderate traumatic brain injury (TBI), also known as post-concussion syndrome (PCS) or chronic PCS with post-traumatic stress disorder (PTSD) secondary to blast injury.

Inclusion Criteria:

• Adults, 18-65 years old
• One or more mild-moderate TBI's characterized by loss of consciousness due to blast injury that is a minimum of one year old and occurred after 9/11/2001
• Absence of acute cardiac arrest or hemorrhagic shock at time of TBI.
• Absence of intracranial neurosurgery post-TBI
• Disability Rating Scale of 0-3
• Negative Michigan Alcohol Screening Test (MAST)
• Negative Drug Abuse Screening Test (DAST)
• Negative urine toxicology screen for drugs of abuse
• Negative pregnancy test in females
• Otherwise good health
• Less than 90% on the Percent Back to Normal Rating Scale

Exclusion Criteria:

• Pulmonary disease that precludes HBOT
• Unstable medical conditions that are contraindicated in HBOT
• Severe confinement anxiety
• Pregnancy
• Other pre-TBI neurological diagnoses
• Pre or post TBI history of substance abuse
• Pre or post TBI history of alcoholism.
• Participation in another experimental trial with active intervention.
• High probability of inability to complete the experimental protocol.
• Previous HBOT
• History of hospitalization for past TBI, stroke, nonfebrile seizures, or any seizure history other than seizure at the time of TBI
• Past or current history of mental retardation (baseline FSIQ < 71.
• Pre/post-TBI history of systemic illness with impact on CNS (P.I.'s decision)