Over €1bn in uncollected taxes are owed to the Revenue Commissioners, according to the Annual Report of the Comptroller and Auditor General.
One third of that money has been due for more than five years.
The report also highlighted that as much €143 million in taxes due was written off as uncollectible by Revenue last year.
Nearly three quarters of that amount related to businesses that have closed down.
The report also highlights the comptroller's concern over the price paid by the Department of Justice for a site for a new prison in north Co Dublin.
The 150-acre site at Thornton Hall, which is located about 5km from Swords, cost €30 million in January last year.
This was the or the equivalent of €200,000 per acre and it was paid at a time when agricultural land in the are was selling at between €20,000 and €30,000 per acre.
The comptroller concluded that the fact that the State openly disclosed that it was the buyer of the land, and that it was intended to locate a prison on the site, was the key reason was the vendor was able to extract such a high price.
The comptroller’s report also found that doctors are being paid far too much for discretionary medical card patients.
Discretionary medical cards are given to people whose income exceeds the threshold for automatic qualification for a medical card but who have special medical needs or circumstances.
In 2001, the Department of Health estimated that there were 20,000 such cards in existence and agreed to pay €2.5 million per year to GP's to cater for them.
The following year it upped the estimate to 75,000 cards and the bill rose to €9.5 million.
The comptroller, however, has found that the total number of discretionary cards has been overestimated by 30,000 for the past five years and that compensation was not due to doctors for a significant proportion of them.
However, the Department of Health has told the comptroller that the issue of the operation of the general medical system was currently before the Labour Relations Commission and that it would be inappropriate to deal with the overpayment for medical card patients outside of that forum.
The issues highlighted in the report will be investigated by the Public Accounts Committee in the coming months.
