NHS Highland has warned that the winter vomiting bug has increasingly affected two of its hospitals and people in surrounding communities.
Visitors to Wick's Caithness General and Inverness's Raigmore are being asked to restrict their visiting.
They have been asked not to visit at all if their families have been affected by norovirus.
Raigmore Hospital has closed two wards temporarily and Caithness General has shut one.
In total, 37 patients and 23 staff are affected at the two hospitals.