The Mater Hospital in Dublin has said that an IT systems issue is continuing, whereby it is unable to access electronic patient records.
The problem arose yesterday and the hospital has said it is not a malicious attack.
The Mater said that a small number of surgical appointments have been deferred today and patients affected have been contacted.
The hospital plans to reschedule these surgeries in the coming days.
The hospital said that all other outpatient appointments are unaffected.
It has asked that the public, where possible, avoid its emergency department and use other parts of the health service.
Patients who present with non-urgent conditions are likely to experience lengthy waiting times.
The hospital's Rapid Injury Clinic in Smithfield has also been affected and is currently closed.
