Tallaght Hospital is urging people to stay away if they can as it deals with an outbreak of the winter vomiting bug.
Emergency services are continuing to operate as normal but people are being asked to postpone patient visits with the exception of visitors to critically ill patients and parents of children in the National Children's Hospital.
No children are allowed to visit either the adult or Children's Hospital.
The restrictions are in place after a number of patients were treated with Norovirus and they will be reviewed on a daily basis.