The Health Service Executive (HSE) gave nearly €1m in payments to private nursing homes even though the invoices were not up to standard.
An internal HSE audit, which looked at 27 private nursing invoices for residents, whose care was subsidised under the Fair Deal scheme, found only six met basic requirements.
The confidential audit of invoices in Carlow-Kilkenny over a month found the majority submitted by the private nursing homes, and accepted for processing, were not sufficient to meet the minimum requirements as set down in the HSE's National Financial Regulation.
The invoices need to include precise details such as the nursing home's name and address, a number, date, tax point,VAT and registration numbers.
Two of the invoices, equating to €110,830 or 12.7pc of the payments to private nursing homes over the month satisfied just two of the necessary requirements.
One of these invoices involved a demand for €109,740 from one nursing home, the investigation by the office of the National Director of Internal Audit found.
The lapses follow revelations in the Irish Independent yesterday showing widespread waste and a lack of value for money uncovered in other audits into staffing and patient transport.
Another audit which examined the procurement in the HSE's computer systems found a lack of evidence to show that it was contracting suppliers offering the best value for money.
It looked at six expensive legacy contracts across three former health board regions but four of the contracts could not be found.
The audit report said the auditors tried to determine the extent to which consideration had been given to the use of the most appropriate supplier.
It showed that "management were unable to provide tender evaluation documentation to conclude on the extent to which the most appropriate supplier was selected on terms that met the best interests of the organisation and represented value for money".
A further separate audit of rostering and timesheet claim verification in the South Tipperary ambulance service from January 2010 to June 2011 found that it was unable to do a detailed analysis because of a lack of substantiating documentation.
This was significant because some of the staff were getting an additional top-up in the form of a shift allowance.
"It was noted that despite subsequent implementation of tighter controls in the latter half of 2011... the audit found there remained deficiencies in the existence, qualify and safeguarding of documentation."