A major review of deaths in custody has found a substantial increase in the number of Aboriginal people dying in custody over the past five years.

The Australian Institute of Criminology (AIC) study found the overall rate of deaths in state and territory prisons has remained relatively steady over the past 20 years.

But there has been a spike in the number Indigenous deaths in custody, in line with an almost doubling of the number of Aboriginal Australians being locked up.

The findings come two decades after the landmark Royal Commission into Aboriginal Deaths in Custody, which made 339 recommendations for reform - most of which have not been implemented.

Around 30,000 people are behind bars, and Indigenous inmates account for a quarter of the prison population but only 2 per cent of the general population.

"It hasn't been getting better, it's been getting worse despite, I think, a lot of attempts by governments and agencies to try and bring that down," AIC director Dr Adam Tomison said.

The National Deaths in Custody Program Monitoring Report has found Indigenous death-in-custody rates have decreased over the past decade but risen again recently.

The report found: Almost 1,400 deaths in prison custody have been recorded since 1980

Almost 1,400 deaths in prison custody have been recorded since 1980 14 Indigenous people died in prison in 2009-10, the highest number on record

14 Indigenous people died in prison in 2009-10, the highest number on record An increasing number of people are dying from heart attack and cirrhosis of the liver

An increasing number of people are dying from heart attack and cirrhosis of the liver From 2008-11, 33 of the 159 deaths in prison custody were Indigenous prisoners

Most of those deaths occur in prisons rather than other forms of custody like juvenile detention and police cells.

In 2008-09, 15 Aboriginal people died behind bars. By 2010-11 that number had risen to 21.

The AIC report shows that most of these deaths were due to natural causes like cancer and heart conditions.

Previously self-harm was the leading cause of deaths in custody.

"Prisons need to be aware of the health needs of older prisoners and to make sure that they're addressed to obviously prevent deaths," Dr Tomison said.

"I guess the good news is that, and especially for the last eight years, Indigenous people in custody have been less likely to die in custody than non-Indigenous people.

"That said though, the number of deaths is still too high."

NT has the highest rate of Indigenous deaths in custody

Based on current statistics, the Northern Territory has the highest rate of Indigenous deaths in custody in Australia.

Between 1979 and 2011, there were 32 deaths in custody in the Territory, 24 of which were Indigenous people.

The Territory has the highest incarceration rate of Indigenous people in Australia, with 97 per cent of juvenile detainees being Aboriginal.

Of adults in prison or other forms of detention, 82 per cent are Indigenous.

The Closing the Gap policy is focused on improving those outcomes for Indigenous Australians.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 4 minutes 36 seconds 4 m 36 s Listen to Martin Cuddihy's report for The World Today Download 2.1 MB

The Federal Government says it is supporting state and territory governments with $4.6 billion.

But Gracelyn Smallwood, an associate professor at James Cook University and an Aboriginal leader in North Queensland, says a lot of that money does not end up where it is needed.

"The infrastructure's very poor and most of the jobs are given to outside consultants which are mostly non-Indigenous people or companies that don't employ people on the ground, which is our local people," she said.

"They've abolished the work for the dole scheme, which was at least helping our communities to get some economic development.

"Closing the Gap is very, very important from a holistic point of view, and once you start cleaning up poverty then everything will start falling into line.

"I'm optimistic that if those recommendations were implemented that we could start closing the gap."

Associate Professor Smallwood says if all the royal commission's recommendations had been implemented, "we wouldn't have any deaths in custody and we wouldn't have a massive increase in the incarceration rates nationally".