Approximately 800 women were not issued with their CervicalCheck results due to a technology issue, the HSE has said.
The tests, most of which were repeat tests for human papillomavirus (HPV), were carried out between October 1, 2018, and June 25 this year.
Results letters were also not issued to some GPs, RTÉ reports.
"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 told RTÉ.
The HSE has apologised for the issue, and for the confusion and anxiety it may have caused.
Due to slower than expected IT updates to a Quest Diagnostics laboratory in Virginia, USA, hundreds of results letters were not issued to women.
"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.
The affected laboratory part of extra Quest Diagnostics capacity secured by CervicalCheck.
The HSE has said that "results are now being issued manually to GPs" until an IT update is completed.
The Department of Health today said the HSE advised it yesterday that it became aware of the IT problem in June.