DERRIFORD Hospital is advising anyone who has experienced sickness or diarrhoea in the past 48 hours to avoid visiting the hospital unless absolutely necessary.
The hospital is attempting to protect patients from illnesses such as the winter vomiting bug norovirus.
A spokesman for the hospital said: "We know it is currently around in our local community and it is highly contagious."
"We are asking all patients and visitors to be aware of what they may unwittingly bring in to hospital with them."
"If you have been in contact with someone who has symptoms you could also be bringing this virus into the hospital."