The HSE's in the process of contacting thousands of patients to reschedule appointments following Friday's cyber attack on its networks.
All outpatient and radiology services are impacted.
However chemotherapy and dialysis services, along with the vaccination programme, are continuing as normal.
Meanwhile efforts are continuing the identify the extent of the attack, and if personal patient data has been stolen.
HSE Chief Operations Officer, Anne O'Connor, says work has also begun rebuilding its IT system: