Young ex-servicemen are three times more likely to kill themselves than their civilian counterparts, a study has suggested.
Veterans aged under 24 are at greatest risk, with those in lower ranks and with shorter careers most vulnerable.
The Centre for Suicide Prevention linked military discharge data between 1996 and 2005 with details of suicides.
The MoD said veterans were entitled to mental health assessments and schemes had been introduced to improve access.
Of the 233,803 individuals who left the armed forces during the study period, 224 took their own lives, the report found.
The suicide risk was highest among young men leaving the armed forces within the first two years of discharge, it said.
The MoD-funded study found veterans had a low rate of contact with mental health professionals in the year before death, 14% for those aged under 20 and 20% for those under 24 years.
But the overall suicide risk was no greater for ex-military personnel than for civilians when all age groups were considered, from 16 to 49 years. Men aged 30-49 years had a lower rate of suicide than the general population.
The report's lead author, Professor Nav Kapur, said they could not prove why the increased rate occurred, but said there were three possible reasons.
One could be those joining the military at a young age were already vulnerable to suicide.
"This would explain why those serving for a relatively short period of time before being discharged were most likely to take their own lives," Prof Kapur said.
A second explanation was the difficulty a minority of individuals experience making the transition to civilian life, he said.
The effect of exposure to adverse experiences during military service or active deployment was a third possibility.
Yet many of those most at risk had not completed basic training and had not deployed overseas, he said.
The risk of suicide was also higher in young women aged under 20 years compared with the general population, but the overall numbers were small.
Prof Kapur, professor of psychiatry and population health at Manchester University, said: "Whatever the explanation for our findings, these individuals may benefit from some form of intervention.
"Initial pre-recruitment interview, medical examination and training are important in ensuring military health but it should be recognised that those discharged at any of these stages may be at higher risk of suicide."
The study compared the military discharge data with details of suicides collected by the National Confidential Inquiry into Suicides and Homicides.
It used mathematical models to compare the figures to the general population.
A spokesman for the MoD said all service-leavers were entitled to a package to help them re-settle.
Extra help was given to those assessed as vulnerable to help them find accommodation, employment and welfare assistance.
Six community mental health centres have been set up to make it easier for veterans to seek help, he said.
"All veterans are also entitled to a free assessment of their mental health at the Medical Assessment Programme at St Thomas' Hospital in London, he added.
"We are also trialling a mentoring scheme to provide individual support to leavers as they re-adjust to civilian life."
The report comes days after Britain's highest-decorated serving soldier criticised the government for failing to help ex-servicemen and women suffering mental health problems.
Lance Corporal Johnson Beharry called on the government to give more help to his comrades suffering from post traumatic stress disorder, depression and mental breakdowns.