US war veterans are twice as likely to kill themselves as ordinary civilians, a study following 320,890 men found.
Vietnam war veterans were included in the survey
Researchers compared data between non-veterans and those who had served at some point between 1917 and 1994.
Men who were white, better educated and older than the other men appeared to be at higher risk, as did those with a physical or emotional disability.
Researchers say the findings emphasise the need for mental health care for those serving in Iraq and Afghanistan.
The research, published in the Journal of Epidemiology and Community Health, included men who had served in World War II, the Vietnam war, the Korean War and the Gulf war.
It said the rate of suicide among men who had taken military service was 2.13 times higher than those who had never served in the armed forces.
War veterans were also twice as likely to use a firearm to kill themselves, it said.
Disabled veterans, or those who had experienced emotional or psychological trauma during their service were identified as the highest risk group.
Interestingly, overweight veterans were less likely to have killed themselves than those of normal weight, the study found.
Although the research did not include data from men returning from Iraq and Afghanistan, authors said the findings had strong implications for them.
Lead researcher Mark Kaplan, of Portland State University in Oregon, said doctors should "scrutinise veterans for signs of suicidal behaviour or thoughts and, if needed, they should intervene to make sure these patients do not have access to firearms".
He said in general "there is inadequate mental health screening, and many of the doctors outside the VA (Veterans Affairs) system are not trained to deal with these sorts of problems and don't have the time to treat them".