A group of Australian academics believe they have finally answered the question of whether bicycle helmets reduce head injuries.

Researchers say they have evidence which shows mandatory helmet laws in New South Wales have worked, slashing head injuries by almost one third.

Australia was the first country to introduce mandatory helmet legislation in 1991, and ever since it has been the subject of fierce debate.

The issue flared last year when Professor Chris Rissel from the University of Sydney found a decline in cyclist head injuries in New South Wales was not due to mandatory helmet legislation, but other factors, like general road safety improvements.

The paper was later retracted by the journal which published it after other academics pointed out errors in the data.

Now those academics have released their own research.

Dr Jake Olivier led researchers from the University of New South Wales and the Sax Institute.

They found that from just before to just after the mandatory helmet law came into effect in NSW, head injuries among cyclists fell by up to 29 per cent.

"The mandatory helmet law apparently did its job. It was set in motion to reduce bicycle head injuries and it accomplished that," he said.

"We were able to isolate a definitive benefit in the mandatory helmet law to the reduction of the bicycle-related head injury."

The researchers looked at the ratio of injuries to cyclists' heads and injuries to arms and legs from the period before the law came in and compared that to the ratio of injuries in the period after.

They also examined pedestrian injuries over that time.

"In those two analyses, the ratio was flat for both, indicating it's not due to road safety improvements," Dr Oliver said.

But Professor Chris Rissel disputes the findings and argues helmet laws should be repealed because they "do more harm than good".

Whether forcing people to wear helmets deters them from cycling is disputed, but Professor Rissel maintains the number of people riding bikes has dropped since the introduction of helmet laws.

"The health benefits to physical activity through more people cycling really outweigh the injury risk that there is," he said.

"If someone doesn't take up cycling because the helmet law is a barrier to them, there is nothing to say that they won't take up something else."

But for bicycle user groups the debate is not the main game.

Bicycle New South Wales vice-president Richard Birdsey says the laws have been a "hugely contentious issue" in the cycling community.

But he says they should stay and the focus should be on road safety.

"We really feel that it is a bit of a distraction in terms of people debating backwards and forwards as to whether they are a good thing or not," he said.

"We'd really want to see the Government, community groups and motoring groups working towards making our roads safer for all road users, including cyclists.

"Many people I speak to on the road say that they like riding without a helmet, others say they would never even dream of getting on a bike without one.

"Certainly I never would and a helmet has saved me on a couple of occasions."