Hundreds of Indigenous Australians with mental health and cognitive disabilities are being warehoused in jails rather than being supported in the community, according to a new study by the University of New South Wales.

The research paints a grim picture of life for more than 670 Indigenous prisoners in the state, tracking their interactions with police and courts for up to 30 years.

All of them suffered from a mental health disorder like depression, schizophrenia, or psychosis; or a cognitive disability such as an intellectual disability, acquired brain injury, or foetal alcohol spectrum disorder (FASD).

Key findings: Study looked at 2,731 prisoners with mental and cognitive disorders. 676 were Indigenous.

Study looked at 2,731 prisoners with mental and cognitive disorders. 676 were Indigenous. Indigenous prisoners had first contact with police at 15 years, compared to 18.

Indigenous prisoners had first contact with police at 15 years, compared to 18. Indigenous prisoners 2.6 times more likely to have been in out of home care.

Indigenous prisoners 2.6 times more likely to have been in out of home care. 2.4 times more likely to have spent time in juvenile justice custody.

2.4 times more likely to have spent time in juvenile justice custody. Indigenous women had average of 23 convictions compared to 15 for non-Indigenous.

The report found these Indigenous prisoners had their first contact with police 3.4 years earlier than non-Indigenous inmates, at about 15 years old compared to about 18.

They were 2.6 times more likely to have been placed in out of home care as a child and they were 2.4 times more likely to have spent time in juvenile justice custody.

Eileen Baldry, Professor of Criminology at UNSW and one of the report's authors, told Lateline most of these people had complex support needs.

"It is absolutely clear that this group of people are put on a train into the criminal justice system because they are being managed from an early age by the police and that is criminalising their behaviour," she said.

The study also found that Indigenous women with mental and cognitive disorders had significantly higher rates of convictions and episodes of incarceration than their male and non-Indigenous peers, with an average of 23 convictions compared to 15 for non-Indigenous women.

Indigenous men had an average of 18.9 convictions to 15.6 for non-Indigenous men.

Broken Hill program helping former prisoners

In Broken Hill, in far western New South Wales, a significant number of Indigenous people have spent much of their lives in the town's prison.

"Most of our clients have spent most of their lives being managed in jails and criminal justice systems rather than actually being supported in the community," said Dr Mindy Sotiri, director of the Community Restorative Centre (CRC), a program to try and help these prisoners once they leave jail.

Dr Sotiri said the centre provides relationship support, helps find housing, fill out forms and gain access to things like Centrelink entitlements.

"Stuff that is really basic, but is the anchor that anyone needs to really live in the community," she said.

The CRC helped former prisoner John Dennis find housing and settle in to the community.

It has now been nearly four years since he was last in prison.

"It was important for me to stay out of trouble. I thought I'd try a different approach and stay out of jail and I've stayed here ever since," he said.

Need for early diagnosis and support

Dr Sotiri said many of the people the CRC helps have some kind of disability but many of them are undiagnosed.

"Looking at the board I can see people who have both cognitive impairment and or mental illness but there are also very few people who have a diagnosis of cognitive impairment," she said.

"It's just clear from working with them that that's the case."

Professor Baldry said Aboriginal did not have the same access to early childhood services that would diagnose and support people with mental and cognitive impairments.

"There needs to be the right kind of support and that is in short supply at the moment. But that can be done. We know how to do it. We do it for other people," she said.

"That could prevent quite a significant number of this group of people ending up in the criminal justice system."