At least €76 million is owed to some of the State's top hospitals by health insurers, according to a report today.
VHI and Bupa (now Quinn Healthcare) are said not to have paid an average of €19 million annually over the past four years because of incorrect billing by hospitals.
The figures, obtained under the Freedom of Information Act by RTÉ Radio, show 50 hospitals are involved and the amount may be in excess €100 million over a longer period.
Hospital administrators who had failed to complete forms to the satisfaction of insurers were sometimes not subsequently dealing with them leading to the shortfall.
Tallaght and St James's hospitals in Dublin had together failed to collect over €21m for the treatment of private patients through the public service over the last four years, the report said.
Waterford Regional had failed to collect €7m.
The report said hospitals blamed the complexity of the handwritten forms insurers required before sending payment.
The Department of Health said it had not been asked to negotiate a new claims processing system and that such a request would have to be addressed to the Health Service Executive (HSE).
It said arrangements for payment were established by the hospitals and the insurers. It also noted insurers insisted on claims being signed and verified by the treating consultant.
In relation to the figures the Department said: It is "unclear whether the sum referred to is in fact a shortfall or reflects delayed payments where the funding is still being pursued".
Minister for Health Mary Harney supported any efforts to obtain any monies owed, it added.
The HSE said it also had not been asked to negotiate a new system for processing claims.
A spokesman acknowledged that a percentage of charges were not collected due to "incomplete data [and] administrative error" some of which become bad debts.
"There are number of reasons for this other than simple default. These will include a patient's inadequate or lapsed cover, pre-existing conditions and disputed accounts," the spokesman said.