The number of patients waiting to be seen at an outpatient clinic for the first time has almost doubled to 340,000 compared with figures released last April.
A new report from the Health Service Executive also shows that 16,600 patients have been waiting four years or more to be seen at a clinic.
It also reveals that a number of hospitals are in severe financial crisis, with five major hospitals over budget by €65m to the end of July.
Minister for Health James Reilly said that when all data is in from hospitals, the number of people waiting to be seen at an outpatient department will rise to around 360,000 people.
Speaking on RTÉ's Six One News, he also said waiting times for inpatient and day treatment had dropped.
Mr Reilly said the priority was to treat the longest waiters first and ensure those who were most ill get speedy treatment.
The hospital facing the biggest overspend is Beaumont Hospital in Dublin, which has exceeded its budget by €17m, before the new cuts announced recently by the HSE have been implemented.
Provisional figures in April put the number waiting to be seen at an outpatient clinic at just below 175,000.
But figures from more hospitals have now been validated and fresh referrals have been made since then, which puts the new figure at 339,441 patients.
These figures relate to 37 hospitals and do not include all acute hospitals and so the HSE admits that the total number waiting is higher.
Over 113,000 patients have been waiting a year or more to be seen.
The HSE Performance Report for July shows that along with Beaumont, there are other hospitals in severe financial trouble, with the Mid Western Regional in Limerick €14.6m over budget.
Galway University Hospitals is nearly €12m over budget, Cork University Hospital is over by €10.3m, while Tallaght Hospital has exceeded its budget by over €10m.
Stephen McMahon of the Irish Patients' Association has warned that hospitals will shortly "run out of cash" and described the waiting list figures as shocking.
The main hospitals where patients are waiting longer than a year to be seen as outpatients are:
- Waterford Regional - 20,945 patients
- Galway Hospital Group - 21,089
- Limerick Regional - 14,263
- Cork South Infirmary/Victoria Hospital - 5,784
- Tallaght Hospital - 5,115 patients
- Our Lady of Lourdes Hospital - 4,577
- Our Lady's Children's Hospital Crumlin - 3,632 patients
- Beaumont Hospital - 2,402
Just over 66% of patients are waiting less than a year from when they were referred by their GP.
The report also shows that 55,425 adults and children are waiting for inpatient or day case treatment, which is down from 57,708 in June.
Of the 55,425 patients waiting, 13,484 are adults and children waiting for an inpatient procedure, while 41,941 are adults and children waiting for a day case procedure.
For the first time, the report includes hospital absenteeism figures, which show that Our Lady of Lourdes Hospital in Drogheda had the highest rate of absenteeism in Ireland in June with 7.4% of staff absent.
The other hospitals with high absenteeism rates were Ennis General and Roscommon County, both with above 7% of staff absent.
The HSE says its latest performance report shows a deficit of €270m, which highlights the "seriousness of the financial challenges" faced by the service.
It said that hospitals now have to bring their patient activity levels back in line with the service plan.
The HSE said that demand for services continues to grow and on average hospitals are treating 7.7% more inpatients than their service plan targets.
It said every line of expenditure is being scrutinised to identify any further areas where savings can be made but minimising the impact on frontline services.
The Chief of the Irish Medical Organisation's GP Committee has said that he is not surprised by new figures from the HSE.
Speaking on RTÉ's Drivetime, Dr Ray Wally said that cutbacks and the recession are taking their toll on the provision of acute and primary care in an outpatient setting.