70% of cyclists treated for head injuries were not wearing a helmet at the time of their trauma.
The research, carried out at the National Neurological Centre at Beaumont Hospital in Dublin, shows that cycling had the highest number of referrals to the facility.
Acquired Brain Injury Ireland says the report is not surprising and it confirms what they already see in their services.
CEO Barbara O'Connell says a helmet can save a cyclists life.
"It is well proven that wearing a helmet reduces the severity of brain injury by absorbing the impact of the collision," said Ms O'Connell.
"So from a brain injury point of view, we want every cyclist - young and old - wearing a helmet.
"It can very definitely be the difference between life and death for a cyclist."
Meanwhile, 70 drivers have so far been detected breaking the speed limit on the country's roads, since Project Edward began at midnight.
32,000 vehicles have been checked for speed as part of "European Day Without A Road Death".
A driver was clocked travelling at 148 in a 120km zone on the M1 at Lusk in Dublin, while another motorist was found to be doing 105km/h in a 80km zone in Dunshaughlin, Co Meath.