As many as 800,000 Australians suffer from Post-Traumatic Stress Disorder (PTSD) at any given time, making it the second most common mental health disorder, new figures reveal.

Meanwhile, medical experts are being urged to pay particular attention to the signs of PTSD in children and teenagers, in whom the condition often goes undiagnosed.

The Australian Centre for Post Traumatic Mental Health estimates that up to 10 per cent of people will suffer from PTSD at some point in their lives.

As such, the centre is launching a new set of guidelines to help medical professionals identify and treat sufferers.

Centre director Professor David Forbes says that rates of PTSD are second only to depression, despite the condition's relatively new status as a diagnosis.

"PTSD is one of the newer diagnoses, and so from that perspective it's taken some time for the recognition of PTSD as a condition to be kind of filter through to the professional and broader Australian community," Professor Forbes said.

"Parents are particularly good at picking up changes in obvious behaviours, but some of the internal mood systems like feeling down, or having memories, or having intrusions of what happened may be less obvious to parents.

"And kids aren't necessarily going to tell their parents about it, which is why it's critical to be interviewing parents and children in relation to traumatic stress.

"The recognition of PTSD is certainly increasing, although perhaps the magnitude of how widespread it is may be not."