Beaumont Hospital in Dublin is urging members of the public not to visit unless it is essential and unavoidable.
The warning is due to an outbreak of the winter vomiting bug, or norovirus.
A hospital spokesperson said today that 42 patients had symptoms of the virus, including severe abdominal cramps, vomiting and diarrhoea.
38 beds are currently unavailable in the hospital as a result of quarantine arrangements.
A statement from the hospital stated the virus is a self-limiting illness, usually lasting between 24 and 48 hours and does not usually require medical treatment.
People with these symptoms should take plenty of fluids and, if they are concerned about them, they should contact their GP.
