The slowest turnover is in Mayo, Galway and Cork
New figures show that 1,126 ambulance calls took more than an hour to hand over patients to hospitals.
The statistics, for May this year, were released to Fianna Fáil health spokesperson Billy Kelleher.
They show that virtually all hospitals continued to miss a 20 minute turnaround time for the majority of ambulance calls.
They reveal just four hospitals managed to meet the 20 minute target for more than half of ambulance attending their emergency departments.
While none of the other 26 hospitals had a success rate of more than 49% for the turnaround.
The best performing hospital according to the figures was Tallaght Paediatric at 58%.
Navan Hospital, Connolly Hospital and St James's were the only others to break the 50% mark.
At the other end of the scale, two hospitals failed to break 10% - with Galway recording an 8% success rate and Mayo at 9.7%.
Another six hospitals were in the 10 to 20% range: Letterkenny, Sligo, University Hospital Limerick, Portiuncula, South Tipperary, Midland Regional Tullamore, Kerry and Cork University Hospital.
And of 20,032 ambulance hospital attendances in May, just 5,820 - or 29.1% - had a turnaround within the 20 minute timeframe.
Some 1,126 ambulance calls took more than an hour, with Mayo worst at 17.3%. This was followed by Galway at 15.3% and Cork at 11.4%.
"It is quite alarming that an ambulance going to either of these two hospitals is almost twice as likely to have to wait an hour or more than to reach the turnaround target," Deputy Kelleher said.
"Of course missing turnaround targets has a knock on effect for the ambulance service as it makes it harder to respond to new call outs in the target time if paramedics are delayed at hospitals.
"Unsurprisingly, many of the hospitals with low turnaround rates also experience overcrowding in their emergency departments.
"The delays in transferring patients are clearly not the fault of the ambulance service. Rather there are symptomatic of the ongoing difficulties in our acute hospitals," he added.