NHS Lanarkshire last night said it had closed wards 12, 18, 20 and 22 at Monklands Hospital in Airdrie.
Three of the wards care for elderly patients and the other, ward 18, is a high dependency unit. The health board said infection control measures have been put in place.
Norovirus causes vomiting, stomach cramps, fever and diarrhoea, and is easily spread from person to person.
The winter vomiting bug affected about 100,000 people over Christmas across the UK.