The first cases of seasonal vomiting and diarrhoea have been recorded by NHS Shetland.
The health authority has urged people to reduce the risk of spreading the illnesses.
NHS Shetland’s nurse specialist Kathleen Jamieson said people, especially children, should remain at home for at least two days to protect the community.
“There are steps that we can all take to reduce the spread of these illnesses,” Ms Jamieson said.
“The most effective way is through regular and thorough hand-washing and staying at home whilst ill and for at least 48 hours after the symptoms have stopped.”
She added that children avoiding school, sports clubs, parties or after-school activities should also be considered by parents.
Anyone who is feeling unwell, or who has had these symptoms, should not visit the hospital or care centres until they are symptom-free for 48 hours.
Norovirus can be particularly severe for someone who is already unwell in hospital, and for older people.
Health officials warned that illnesses like norovirus are more common in the winter, although it can occur at any time.