A monkey called Manuel has been stolen in a raid on a caravan.
The common marmoset was taken from the Ropewalk caravan site on Tolney Lane, Newark, between 2100 and 2210 GMT on Friday 5 January.
Manuel's owner and her children are said to be extremely upset and are concerned for Manuel's wellbeing as he has special dietary requirements.
Police say the monkey is likely to be very frightened and may become aggressive if handled by strangers.
Manuel has two white tufts of hair at the sides of his head, and a white blaze on his forehead.
He has greyish fur with darker stripes and his tail has darker coloured rings. He is between eight and 10 inches long (20 to 25cm) and he weights about 14oz (397 grams).
Nothing else was taken in the burglary.
Police are appealing for the public's help to trace the monkey.