From 2000 through the first quarter of 2012, 244,217 service members sustained a traumatic brain injury (TBI) according to the Defense Department. The majority of those reported TBIs were mild TBI, also known as concussion,
and occurred in the non-deployed setting. Most individuals who sustain a mild TBI experience a complete resolution of symptoms within the first several days to weeks after the incident.
http://www.dcoe.health.mil/Content/Navigation/Documents/About%20TBI.pdf