An outbreak of viral infection has led to the cancellation of all non-emergency operations at Beaumont Hospital in Dublin.
Two wards have also been closed to new admissions and, as a precautionary measure, the public has been urged not to visit patients for the next few days.
A hospital spokesman said four cases of small round structured viruses (SRSVs), also known as "winter vomiting virus", have been confirmed at Beaumont.
A number of other possible cases are being monitored, the spokesman added. Among measures taken to prevent further cases are the cancellation of all non-elective procedures and restrictions on visiting patients.
The situation has placed additional pressure on the hospital's accident and emergency department. It deals with up to 40 cases daily.
The spokesman urged people to attend their GPs where possible rather than add to the pressures.
"We are taking all the appropriate steps in the interests of patients and our request that people not visit the hospital any more than is necessary is part of that," he said.
The hospital regretted having to postpone non-elective procedures and all affected persons would be notified of rescheduled appointments, he said.
