Over 64,000 ambulances spent over an hour at a hospital last year, before offloading a patient and getting back on the road.
It's nearly one in every four ambulances that arrived at hospitals.
According to freedom of information figures, the 'turn-around time' was over five hours in 165 cases.
David Hall, the chief executive of Lifeline Ambulance Service, says the delays are caused by congestion at emergency departments.
"Ambulances being tied up outside emergency departments is inhumane, it puts patients at risk, it's very bad for staff.
"Ultimately for the community they are down a resource, because the Ambulance Service, the Fire Brigade and the HSE have not replaced those ambulances, despite their own data showing categorically these delays at the emergency department, taking emergency ambulances out of circulation and putting the community and patients at risk."
