More than 40 cases of the winter vomiting bug have been confirmed over the past three weeks at St John's Hospital in Sligo.
The cases are among patients and some members of staff at the hospital, which caters primarily for older people.
The Heath Service Executive - North Western Area says that precautions have been put in place to control the spread of the bug and these are working satisfactorily.
However, the HSE has requested the co-operation of the public in restricting visiting to essential visiting only, particularly at the weekend.
Visitors are requested to visit one patient only and not to move around the hospital.
