There has been a dramatic increase in PTSD claims for Vietnam Veterans:
In the past five years, the number of veterans receiving compensation for the disorder commonly called PTSD has grown nearly seven times as fast as the number receiving benefits for disabilities in general, according to a report this year by the inspector general of the Department of Veterans Affairs. A total of 215,871 veterans received PTSD benefit payments last year at a cost of $4.3 billion, up from $1.7 billion in 1999 -- a jump of more than 150 percent.
Experts say the sharp increase does not begin to factor in the potential impact of the wars in Iraq and Afghanistan, because the increase is largely the result of Vietnam War vets seeking treatment decades after their combat experiences.
I recommend reading the whole article; there is a good discussion about the large number of Veterans who are not being treated for their PTSD, as well as a discussion about the financial implications of a diagnosis of PTSD for an individual Veteran sometimes leading to exaggeration of symptoms or an unwillingness to get well (which is often unconscious)