There has been an outbreak of the winter vomiting bug
The emergency department at Beaumont Hospital in Dublin is asking patients and visitors to stay away.
It says the department has experienced a high number of patients over the past week.
It adds that this has been further exacerbated by an outbreak of Norovirus - better known as the winter vomiting bug - and flu.
This is resulting in longer waiting times in the emergency department.
The hospital is asking that patients who may be considering coming to the emergency department contact their GP first and, if possible, avoid or delay visiting.
The hospital says it "acknowledges and regrets" the difficult conditions for both patients and staff.
The Beaumont emergency department is one of the busiest in Ireland, providing services to over 50,000 patients each year.