Almost 110,000 hospital appointments have been cancelled this year.
According to Freedom of Information figures obtained by Newstalk, it includes nearly 14,000 in the Mater Hospital in Dublin.
The HSE says there are several reasons why hospital inpatient and outpatient appointments are cancelled.
They could be called off by a consultant or patient, or because there is no bed available.
Many have been cancelled due to industrial action, storms, or a cyber-attack - while thousands did not go ahead earlier this year because of a surge in COVID-19.
In total just over 6,000 in-patient admissions have been cancelled this year, and nearly 104,000 outpatient appointments.
Stephen McMahon is from the Irish Patients Association.
"This is not a case of patients not turning up, this is the system actually saying they're cancelling those appointments," he said.
'More over the winter'
Donegal GP Ciarán Ó Fearraigh said hospitals are struggling to cope with demand.
"We saw recently, here in Letterkenny where I am, inpatient procedures having to be cancelled because of congestion in Emergency Departments.
"I suspect that that's something that we're going to see more and more of over the winter.
"The capacity of the health service, then, also starts to contribute to these problems", he said.
Just under 14,000 appointments have been cancelled in the Mater Hospital in Dublin this year.
Other areas with large numbers include the university hospitals in Limerick and Cork - both with over 7,600.