Nearly 1 out of 5 combat soldiers are leaving Iraq with a mental health problem, such as post-traumatic stress disorder, suggests a landmark study published in today's New England Journal of Medicine. It is the first large survey on front-line forces' mental health.

The numbers probably are slightly higher than the study shows because the severely wounded and others who have been removed from units weren't included, say the study's co-authors, Army Col. Charles Hoge, a psychiatrist, and Army Lt. Col. Carl Castro, a psychologist, of the Walter Reed Army Institute of Research. Most servicemen with mental disorders aren't getting treatment, and a key reason is fear of stigma, they say.

The anonymous survey of 6,201 Army and Marine servicemen deployed to Iraq and Army troops sent to Afghanistan shows higher rates of post-traumatic stress disorder (PTSD), major depression and generalized anxiety for the troops serving in Iraq.

About 16% of Marines and 17% of Army soldiers had symptoms of mental disorders three to four months after combat in Iraq. After Afghanistan duty, the rate was 11% for Army troops; no Marines in the study served in Afghanistan.

The military should fully integrate mental health care into medical clinics instead of having some separate offices for therapy; train soldiers to recognize signs of mental disorders; and use more therapists who are independent of the military, the study's authors say.

The services are trying to identify soldiers with mental health concerns after combat for early treatment, says William Winkenwerder Jr., assistant secretary of Defense for health affairs. Also, extra mental-health specialists are joining units in Iraq, says Lt. Gen. James Peake, the Army's surgeon general.

Today's returning soldiers may recover more easily than Vietnam veterans because the latter were more vilified at home, says psychiatrist Matthew Friedman, executive director of the National Center for Post-Traumatic Stress Disorder.

On the other hand, Gulf War research shows that PTSD prevalence can rise sharply during the two years after combat, Friedman says. And the study doesn't include National Guard and Reservists called up for duty, who had much higher levels of PTSD than active military after the war, he says.

But many in the Guard and Reserves are older, "and the older you were when you went to Vietnam, the less likely you were to come back with psychological problems," says Jonathan Shay of the Boston Veterans Administration.

It's hard to compare current soldiers with Vietnam veterans, who weren't studied until 10 to 20 years after the war; 15% of male soldiers had PTSD, and 30% reported PTSD symptoms during their lives. For troops a few months after Iraqi combat, 13% of Army soldiers and 12% of Marines had PTSD. Also, the Vietnam studies included any veterans of the war, and the Iraq survey includes only combat troops.

Some experts had speculated that about one-third of Iraq veterans could develop PTSD, says Harvard University psychologist Richard McNally. The new findings "suggest a degree of resilience for these soldiers in Iraq that some would not have expected."