Health officials have asked people not to make hospital visits if they have had sickness or diarrhoea in the previous 48 hours.
NHS Greater Glasgow and Clyde (GGC) said people ignoring the advice could end up passing on symptoms to patients.
The appeal is part of wider attempts to minimise the effects of norovirus in hospitals across the area.
Visitors are also being reminded about the "importance of hand hygiene when entering and leaving" hospitals.
Prof Craig Williams, lead infection control doctor at NHS GGC, said: "We understand that when a relative or friend is in hospital you want to offer them comfort and support by visiting them.
"Unfortunately visiting a loved one if you have experienced sickness and diarrhoea in the last 48 hours can have consequences for the person you are visiting. They would potentially catch whatever infection you have leading to their health being compromised.
"We are asking people not to visit friends or relatives in hospital if they have experienced any sickness or diarrhoea in the last 48 hours."
Prof Williams added: "Norovirus is particularly prevalent during the winter and it's not unusual to see this type of virus in the community.
"We want to minimise the number of patients experiencing norovirus and not have symptomatic friends and relatives visiting."
Norovirus, sometimes known as the winter vomiting bug, is the most common stomach bug in the UK.
The virus is highly contagious and can affect people of all ages.
There's no specific cure for norovirus. It is usually mild and usually lasts a few days.