Pentagon figures show 40,000 U.S. troops have been diagnosed with post-traumatic stress disorder since 2003. But officials believe many more are keeping their illness secret.

Army Surgeon General Eric Schoomaker says officials have no reliable figures on how many troops have PTSD or how many have sought treatment for it after serving in the wars in Iraq and Afghanistan.

That's because officials are encouraging troops to get help — even if they go to civilian therapists and don't report it to the military. The 40,000 cases are only those the military knows of.

Many troops don't report getting treatment — or don't get help — because they're embarrassed or fear it will hurt their careers. Marines and Army soldiers have been the hardest hit.