Almost half of hearing aid audiologists working in Ireland have no relevant professional qualifications or have done "questionable" internet courses, according to the Irish Association of Hearing Aid Audiologists.
As a result hundreds of people may have had a hearing problem misdiagnosed.
A European directive came into effect in 1998 to regulate the prescribing and fitting of hearing aids but this has not been enforced by the Department of Health, according to the association.
At present, there is no register of professional audiologists in Ireland, unlike most European countries, and as a result custom-made hearing-aid manufacturers cannot check whether the person who has made an order has a relevant professional qualification, said Jim Sharkey, association president.
The European Communities (Medical Devices) Regulations 1994 regulated the prescribing and fitting of custom-made hearing aid inserts and moulds. It specified that these should only be made for a patient in accordance with a prescription from a person with a relevant professional qualification.
This regulation came into effect in Ireland in June 1998 but because no register exists it could not be enforced, Mr Sharkey said. The association has been lobbying for a register since 1987.
"We have 68 members. We estimate that there are approximately another 65 people working as hearing aid audiologists with no qualifications at all or qualifications attained over the internet. But we believe the vast majority of these people have no qualifications at all," said Peter Ferguson, secretary of the association.
"Some people are buying a quick two-week course over the internet and hanging their certificate on the wall. We have begun to notice this happening within the past few months," said Mr Sharkey.
The biggest danger of unqualified people is that they might miss a serious medical problem, such as a tumour, Mr Sharkey said. A hearing aid with an inappropriate pitch could also cause further damage. The National Association for Deaf People said it had received complaints about unqualified audiologists from members.
When contacted, the Department of Health declined to comment on the issue.