The final cause of death will be determined by the coroner, but the state pathologist confirmed that there were no suspicious circumstances surrounding the death, and that death most likely occurred as the result of a medical condition.

Standard procedure toxicology reports, which will take some time to be complete, will be relied upon to confirm the findings.

A 23-YEAR-OLD man died of natural causes at Risdon Prison on Friday night - the third death in custody in two months.

Director of Prisons Brian Edwards said the death was suspected to be the result of a medical condition and that investigations indicated there were no suspicious circumstances.

He said police, the government pathologist and the coroner had reviewed the scene and that police would prepare a report for the coroner.

"This is standard practice when a death occurs in a corrections environment," he said.

Prison Reform and Action Group spokesman Greg Barns said it was important the investigation was transparent and addressed the Hobart prison's treatment of congenital conditions.

"Prisoners are some of the most vulnerable people in our society and the measure of any society is it how it treats those people," he said.

Premier Will Hodgman extended his condolences to the man's family.

"There are significant commitments on prisoner welfare and that includes for those who have mental health issues, we need to treat them very seriously and their welfare is paramount but needless to say we're always looking at how we can do things better and more effectively," he said.

The man's death is the third in custody since June.

South Australia doctor Robin Michael was found dead at Risdon Prison on June 29.

The 63-year-old was in remand in Risdon after pleading not guilty to allegedly murdering his wife Kerry Michael while the pair were on holiday in Tasmania.

Wynyard man Troy Collin Monson, 42, died while inside a prison van while being transported from Launceston to Hobart.

Mr Monson and Mr Michael are believed to have taken their own lives.

Coroner Simon Cooper has launched an inquest into the deaths of both men.