Nearly 18,000 people over the age of 75 have been on a hospital waiting list for at least 18 months.
Hospitals in Limerick, Galway and Cork are worst-affected.
A total of just under 87,000 people over the age of 75 are on waiting lists, in hospital around the country.
They are waiting for inpatient or outpatient appointments or procedures.
Nearly 26,000 have been waiting over a year - and of those, 17,817 are waiting at least 18 months.
Sinn Féin's health spokesman, David Cullinane, says the figures are extraordinary.
Of those over 75 waiting at least 18 months, 2,520 are waiting for treatment in University Hospital Limerick - the worst in the country.
That's followed by 2,286 in Galway University Hospitals, and 1,747 in Cork University Hospital.