Around 800 women who underwent CervicalCheck screening were not issued with their results due to what the Health Service Executive has said was an IT issue.
The HSE said it sincerely apologised for the issue, and the confusion and considerable anxiety it may have caused for some women.
Results letters were also not issued to some GPs.
The tests were carried out between 1 October 2018 and 25 June this year and were mainly repeat tests for human papillomavirus (HPV).
The HSE has said that a small number of tests affected by the issue have also been identified outside of this time period.
The problem arose in one Quest Diagnostics laboratory in Chantilly in Virginia in the US, which the HSE said was quality assured and part of extra Quest Diagnostics capacity secured by CervicalCheck.
Due to slower than expected IT updates to this laboratory, to allow results to be sent to women and GPs, around 800 results letters were not issued.
The HSE has said that an IT update was taking place at the laboratory and "results are now being issued manually to GPs until that is completed".
The problem was discovered after a woman recently raised concerns about a delay in getting the results of her CervicalCheck test.
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"The existence of an IT issue was identified following engagement with the Department of Health in relation to representations from a woman using our services," the HSE said.
Some GPs and practice nurses have also reported in recent days that they have not received CervicalCheck result reports.
CervicalCheck has asked Quest Diagnostics to issue these reports manually, which Quest has said will happen today, pending the IT issue being resolved.
The Department of Health said today that the HSE advised it yesterday that it became aware of the IT problem in June.
Yesterday, RTÉ News put a series of questions on the issue to both the HSE and the department.
The tests involved were primarily repeat HPV tests, which were being done because previous tests were carried out by Quest outside of the recommended timeframe.
The department said today that the HSE has advised that it was working to ensure that all women and GPs were informed of results and that it expected this process to be completed in the coming days.
The HSE said that all necessary updates and testing to ensure electronic results are issued to women and GPs will be finalised in the next two weeks.
"We are closely monitoring and engaging with the laboratory in this regard", it told RTÉ News.
The HSE has described the matter as a limited incident.
"We have identified approximately 800 women who were regrettably not issued with a results letter," said Frances McNamara, head of the HSE National Screening Service.
"In response on 1 July, CervicalCheck wrote to these women identified and advised them to contact their GP to receive their results."
When a woman's CervicalCheck screening test is processed by a laboratory, results of the test are transferred to the Cervical Screening Register.
After this, the woman's GP should receive electronic notification of the results and the woman should receive a letter that her result is available and information on the next step.
The HSE said that its priority is to ensure that the women involved are kept informed and receive their results promptly.
It said it is closely monitoring the matter and engaging with the laboratory.
The patient representative on the CervicalCheck steering committee, Lorraine Walsh, has said she is "flabbergasted" at the latest revelations.
Speaking in Galway this evening, Ms Walsh said it was shocking to think that such "unnecessary" delays were being experienced by women around the country.
She said she was disappointed for herself and the system, but most of all for the women of Ireland. She said it was hard to see how people could have confidence in the system when issues kept emerging.
Ms Walsh said it was hard to comprehend the serious communications failures that had occurred.
She described this as "unforgiveable" and said it was something that would further erode confidence.
Ms Walsh said that many people were working to provide reassurances about the screening systems in place, but it was hard to know if lessons were being learned.
Additional reporting Pat McGrath