Nearly 12,000 patients have had their admission to hospital for treatments such as surgery cancelled between March and September this year.
Although there is a range of reasons for this, the most common problem is that the bed the patient due admission was going to be placed in had to be given to a patient who came through the hospital emergency department.
A lack of intensive care beds can also lead to cancellations because they are already occupied, leaving patients who will need to be admitted after surgery, waiting longer for their operation.
The cancellation can cause major upset and inconvenience as well as being very disruptive for someone who badly needs to have an operation or test.
The figures, supplied by the HSE, reveal that hospitals with the most overcrowded and busy emergency departments also had the biggest number of cancellations.
They include St James's Hospital (5,289), Our Lady's Hospital for Sick Children Crumlin (2,432), Beaumont Hospital(2,165), Cork University Hospital (1,228) and Tallaght Hospital (889).