New figures from the HSE show there are 161 doctors working as consultants in public hospitals without fulfilling the criteria to be described as a specialist or consultant.
A breakdown of the figures provided to the Fianna Fáil TD Stephen Donnelly shows that 44% of the consultants working in the mental health services in the Midlands were non-specialists.
In South Tipperary General Hospital, 31% of consultant positions were filled by doctors who had not fulfilled the necessary criteria to be described as a consultant.
Speaking on RTÉ's This Week, Dr Laura Durkan, Vice President of the Irish Hospital Consultants Association, said it was "quite frightening" that so many patients were being treated by doctors who are employed as consultants, but who do not have the required specialist training.
"It's quite frightening, these people are in posts across almost all of the HSE hospitals and they will be doing things like putting people to sleep and dealing with complex medical and mental health issues and they haven't fulfilled the minimum requirement to practice as independent practitioners or consultants, so patients should be quite concerned," she said.
"This is a reflection on the fact that we have half the number of consultants that European figures would suggest we should have. And 20% of posts are unfilled across the board.
"The issue with non-specialist consultants is quite scary... They are doctors but they don't fulfill the criteria required to be described as specialists or consultants" added Dr Durkan.
The figures show that 13% of consultants working in the Midlands Regional Hospital in Tullamore and 12% at University Hospital Kerry do not have specialist qualifications.
In Sligo University Hospital, the figure is 11%, while in University Hospital Waterford it is 7%.
The HSE said patient and public safety is paramount within the health service, and a number of organisations are "actively working in partnership with the HSE to resolve the complex underlying issues around the recruitment of Specialist Consultants nationally."
A spokesperson said a working group has been established between the HSE, the Medical Council and the Forum of Postgraduate Medical Training bodies to examine the issue.
The Department of Health said: "Any doctor who occupies a consultant post, even if he/she is not on the specialist register still holds a medical licence and is on a division of the Medical Council Register.
"They are therefore fully qualified to practice medicine, though not as consultants," said a spokesperson in a statement.