St. Vincent's University Hospital in Dublin has confirmed that 18 patients are suffering with symptoms of the "winter vomiting virus".
The hospital has announced a number of measures to stop the spread of the Norovirus bug to other patients and visitors to the hospital.
The hospital has appealed to the public to attend accident and emergency at the hospital only if strictly necessary.
Visiting has also been curtailed, and parents have been advised not to bring children to the hospital.
The presence of the virus has been confirmed on one ward, and patients on three other wards are displaying the symptoms.
