Nearly 46,000 people abandoned their visit to an emergency department last year, without completing their treatment.
Some of these patients are frustrated by long delays, while others go elsewhere for treatment or go home.
This new data has been released to Newstalk by the HSE under the Freedom of Information Act.
It shows the number of patients who did not wait to get treatment after presenting in emergency departments, or left before completing their treatment.
A total of 45,587 people fell into this category last year.
The highest number was in the Mater Hospital in Dublin, at over 5,200 - nearly 500 ahead of Tallaght University Hospital.
Four other hospitals had over 2,000 'did not waits' last year - St James's in Dublin, Our Lady of Lourdes in Drogheda, University Hospital Limerick, and Connolly Hospital in Dublin.
Stephen McMahon, from the Irish Patients Association, says the new figures are very concerning.
He said: "It's a very serious issue, because people can deteriorate and get sicker.
"Was it the fact that COVID-19 [made them] afraid of getting the virus, or was it there were very long delays for them to be seen because the staff were occupied and dealing with COVID-19?"
The HSE says in January of this year, 3.2% of emergency department patients did not wait for treatment - 3% less than two years earlier.
Data has previously shown that long waiting times in emergency departments remain a problem for most patients.