Over 11 thousand patients were admitted to hospital without a bed in April according to figures from the INMO.
University Hospital Limerick was the worst affected, with 1 thousand 971 patients admitted without beds.
It was followed by Galway University Hospital, CUH in Cork, St Vincent's in Dublin and Letterkenny University Hospital.
The nursing union says this level of overcrowding during a month that's "traditionally quieter is a clear indicator that the HSE's current plans are not working".
