There were 624 people waiting on a bed at University Hospital Waterford in November.
That comes as 91,147 patients were on trolleys for the first 11 months of the year, representing record levels.
Figures from the INMO show a 95 per cent increase on the first eleven months of 2007.
However, November saw a slight reduction in hospital overcrowding compared with 2016 figures, down 7 per cent.
The hospitals with the highest number of patients on trolleys, in November were:
University Hospital Limerick: 878
University Hospital Cork: 651
University Hospital Waterford: 624
University Hospital Galway: 539
Letterkenny General Hospital: 502.