It was decided to contact patients after a quality assurance process
Dozens of colonoscopies are to be reviewed at St Columcille's Hospital at Loughlinstown in Dublin.
The Ireland East Hospital Group say colonoscopies performed at the hospital between November 2017 and April 2018 were reviewed as part of a quality assurance process.
As a result, it was recommended that 65 patients be scheduled for a repeat procedure.
Dr Garret Cullen, clinical lead for endoscopy at the Ireland East Hospital Group, says this process was "a precautionary measure" and that the risk to patients was low.
"We acknowledge that patients may be anxious about being called for an appointment but I want to reassure them that this is purely a precautionary measure, appointments are currently being scheduled and we expect this process to be complete within four weeks".
The patients identified have been contacted by the hospital, as have their referring doctors.
This evening, Fianna Fáil's health spokesperson Stephen Donnelly commended the "member of staff who came forward and raised these concerns with management."
“The main priority must be to ensure all patients impacted by this are re-examined as soon as possible," he said.
"However we also need answers as to why this system failure went unnoticed for so long.
“Minister Harris needs to provide a guarantee that all of the necessary steps have been taken to prevent this issue from arising again. Patient safety cannot be put at risk."