A Tasmanian coroner is urging parents not to co-sleep with their babies after an investigation into the death of an infant two years ago.

The two-month-old baby boy died in August 2016 in northern Tasmania while sleeping on a double mattress with his mother and five-year-old sister.

A coronial investigation report said the baby's parents had decided that the whole family would sleep in the lounge room the night of his death because the bedrooms were cold.

The next morning the mother was unable to wake the baby boy and found blood on his face and he was unable to be resuscitated.

A forensic pathologist found the boy was normally developed, nourished and hydrated and found the cause of death was "unexpected death in infancy whilst co-sleeping with an adult and an older child".

In the investigation report, coroner Simon Cooper said there had been a reduction in sudden unexpected deaths in infancy in Tasmania.

But he added: "These deaths comprise a high proportion of potentially preventable deaths of children under the age of 18 years."

"Tragically, they are still occurring on a frequent basis."

Mr Cooper recommended that parents and older siblings do not sleep in the same bed with babies and to always place them on their back in their own cot to sleep.

In previous findings, Coroner Olivia McTaggart said advice to parents not to sleep with their infant was not getting through to many people in the community.

'Any death is one too many'

Tasmania currently has the second highest death rate from Sudden Infant Death Syndrome (SIDS) in the country, behind the Northern Territory.

SIDs and Kids Tasmania executive officer Sharon Davis said the numbers of deaths had reduced significantly in the past 30 years.

"We have between nought and six deaths per year now. We've reduced the numbers down from around 30 deaths a year back in the '80s and '90s," she said.

"We've reduced it by about 85 per cent … but still any death is one too many."

Ms Davis said babies should sleep on their back in a cot.

"Keep their head and face uncovered and to keep their baby smoke-free environment," she said.

"The safest place for the baby is in the cot. We also encourage people to breast-feed their babies.

"Parents need to be very aware of the climate changes because over heating or under heating isn't good either."