The idea that traumatised people, especially the victims of child sexual abuse, deliberately repress horrific memories goes all the way back to the 19th century and the theories of Sigmund Freud himself.

But now some experts are saying the evidence points the other way.

Professor Grant Devilly, from Griffith University's Psychological Health research unit, says the memory usually works in the opposite way, with traumatised people reliving experiences they would rather forget.

"It's the opposite. They wish they couldn't think about it," he said.

In an "Amicus Curiae" (Friend of the Court) briefing to the California Supreme Court, Professor Richard McNally from Harvard University described the theory of repressed memory as "the most pernicious bit of folklore ever to infect psychology and psychiatry".

He maintains false memories can easily be created by inept therapists.

"The stress hormones that are released during a trauma tend to consolidate the memory, make it rather strong and sometimes even intrusive, as you see in post-traumatic stress disorder," he said.

But Professor McNally says some abuse victims do suffer when they reassess childhood experiences much later.

"Seeing the event through the eyes of adult, they realise what has happened to them and now they experience the emotional turmoil of trauma," he said.

The good news is that now, Professor McNally says most victims can be helped.

"Things have changed, happily. We now have treatments that work," he said.

Soldiers returning from war zones, victims of violent crime and sexual abuse, can now be helped by cognitive behaviour therapy, where they learn to assign terrible memories to the past, instead of them crowding their present and future.

Professor Devilly says the therapy is working.

"We're now getting, at the end of between 8 and 12 sessions, 90 to 92 per cent of people no longer meet the criteria for PTSD," he said.

Now psychologists are working to fend off post traumatic stress in high-risk occupations, by teaching recruits to develop resilience.

Editor's Note: (September 27) Following a complaint, ABC News agreed this story lacked balance. There continues to be controversy among relevant experts over recovered memory, and a response from those who support the theory should have been sought. The report also incorrectly stated that Professor Richard McNally had provided a "briefing to the US Supreme Court".