Military Times is running a story about TBI in the VA:

About 6 percent of Afghanistan and Iraq war veterans seeking treatment at Department of Veterans Affairs hospitals have been diagnosed with traumatic brain injuries, according to preliminary data released Friday.

A VA mandatory screening program that took effect in April has looked at 61,285 veterans of the wars. Of those, 19.2 percent were identified on the screening questionnaire as potentially suffering from traumatic brain injuries and were referred for more tests.
...
Aikele said it is too soon to draw any conclusions from the screening because the program has been under way for only a few months. Until there is more screening and evaluation, VA officials do not want to jump to any sweeping conclusions about brain injuries, she said.
...
However, the 5.8 percent figure appears low. The Defense and Veterans Brain Injury Center, a joint Pentagon-VA research effort, 14 percent to 20 percent of troops in previous conflicts have had traumatic brain injuries. The Center says there are reasons to expect a higher percentage among troops in the current conflicts because improved body armor has made them more likely to survive injuries that would have been fatal in previous wars, and because of the prevalence of roadside bombs and rocket-propelled grenades to attack U.S. forces. The blasts from such weapons can easily cause concussive brain injuries.

Comment: The story is discussing a screening test. From what I understand the gold standard for diagnosing TBI is neuropsychological testing. This is a 2 day battery of testing including 1:1 assessment with a doctorate level psychologist. Another point for discussion is the lack of baseline data. What was the service member's cognitive functioning like before the deployment? Finally are PTSD and TBI comparable in any way? Some studies have suggested that PTSD patients have decreased hippocampal volume. Are both a brain injury?

Reference: http://www.militarytimes.com/news/2007/11/military_TBI_numbers_071102w/