More than 233,000 service members sustained a TBI between 2000 and 2011, of which more than three-quarters were categorized as mild.
These statistics include service members injured on the battlefield ("in theater") and in non-combat settings and is a good reminder that asking about a history of concussion/mTBI should not be limited only to a service member's deployment experiences.
Moderate and severe TBIs, including penetrating cranial injuries, are usually diagnosed at the time of injury; their diagnosis requires a period of unconsciousness of more than 30 minutes and post-traumatic amnesia that lasts longer than a day. What you are most likely to encounter in your civilian practice is concussion/mTBI.