Cows on a farm in Surrey have been found to be infected with a highly dangerous disease.
60 animals on the farm near Guildford in the south of England have tested positive for foot and mouth disease.
Foot and mouth can easily be passed on between farm animals so all the cows on the farm have had to be put down.
Experts say there is no risk to humans or pets and are asking farmers across the country to keep an extra special eye on their animals.
The last foot and mouth outbreak in the UK was in 2001. Lots of farms went out of business because so many animals had to be put down.
Vets and other experts are working really hard to make sure the disease doesn't spread and no more animals have to be put to sleep.
Up to date
The Prime Minister, Gordon Brown, has cut short his holiday so he can keep up to date with what is happening.
He said the authorities were doing everything they could to find out where the disease had come from.