The figures for May set a new record and compare to 507,507 on the waiting list in April.
There is growing fears about the risks faced by thousands of very ill patients who are being denied a timely specialist appointment.
Some 44,029 of these are children and of these more than 10,000 are waiting in excess of a year and half.
The numbers waiting for surgery last month reached 78,596 a slight fall compared to April.
But the longest waiters – who are in the queue for over eighteen months – rose to 5,929.
The disappointing figures follow the pledge by the Government to reduce waiting lists by investing €55m in outsourcing patients to private hospitals and making more use of spare space in public hospitals.
But it is having little impact on figures.
There are 18,714 waiting for an endoscopy procedure, more than 700 of whom are in the queue for more than a year.