One patient has tested positive at Raigmore Hospital in Inverness, but there are eight displaying symptoms.
As a result, Medical Ward 2A has been closed.
The bug causes diarrhoea, nausea and vomiting and spreads in the air, making it extremely difficult to contain.
Dr Jonty Mills, consultant microbiologist for NHS Highland, said: “As well as restricting visiting to the affected wards we are also asking people not to come to the hospitals to visit if they have had any vomiting or diarrhoea within the previous 48 hours.
“By doing this we will be able to limit the spread as much as possible.
“Hospital staff will of course be very happy to talk to visitors on the phone so they can get updates on how their relatives are.”
There is no specific treatment for norovirus. NHS Highlands said the best course of action is to stay at home, take paracetamol to relieve symptoms of any fever and to drink plenty of water to prevent dehydration.