Galway woman Lorraine Walsh says she resigned as a patient representative on the cervical check steering committee, due to questions she had over the accuracy of the report released into the controversy.
She says she's "upset and concerned", and stepped down because she doesn't have confidence in the report.
UK experts found original test results carried out on the slides of 308 women with cancer were wrong - 159 of those also had missed opportunities for diagnosis.
The 221 plus group, set up to oversee changes in the Cervical Check programme, says it has concerns around the accuracy of the report.
Ms Walsh made the announcement late last night: