The Department of Health and Social Care says it's written to 157 patients who've been waiting too long for a second endoscopy appointment.
It says they were identified as medics went back through more than 300 cases - and those affected had been offered prioritised appointments before the end of August.
Minister for Health and Social Care, Kate Beecroft MHK, apologised for the delays - which she described as both concerning and disappointing.
She says the average waiting time for a routine endoscopy appointment is currently 33 weeks - which she called 'wholly unacceptable', adding it could be a risk to patient safety.
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