THE federal government admits it doesn't know how many of the nation's soldiers will suffer from mental illness when they return from Afghanistan and other wars.
Australia is to bring home most of its troops from Afghanistan, as part of the widespread drawdown of Western troops, by 2014.
But there are concerns that many will return nursing major mental health issues - with some symptoms likely to take years to surface.
As of June 30 this year, almost 44,000 troops have been deployed to the Middle East, with 964 having since been medically discharged, the Minister for Defence, Science and Personnel, Warren Snowdon, said.
Of those, 440 were discharged for conditions related to mental health.
Close to 70 per cent of that number were assessed to be suffering as a direct result of their deployments.
Mr Snowdon said the government doesn't know how many troops will suffer mental illness in the future.
''What we don't know is for all those who have served on overseas operations, and I include navy personnel involved in border protection, exactly how their military service might affect their future health in the decades to come,'' he said.
''This is particularly the case with mental health issues.''
Mr Snowdon, speaking to the RSL national conference in Sydney yesterday, said there was still a great stigma attached to mental health issues but he was heartened by the progress being made to tackle the problem within the Defence Department.
Mr Snowdon suggested more money would need to be spent tackling defence mental health issues after 2014.
''We're already devoting additional resources to those things and we'll continue to monitor that performance,'' he said.
The RSL's NSW president, Don Rowe, said he anticipated an increased demand on his organisation's services as troops return home.
''There is a need out there to provide strong and powerful resources to them, to ensure they are looked after, to ensure that they're able to return to society,'' Mr Rowe said.
''They're young men and young women and they deserve to enjoy a full and fruitful life.''