If you've had it, you'll probably remember how itchy and scratchy it was.
We're talking about chickenpox - the illness that leaves you covered in spots and often spreads quickly among friends when one of you gets it.
It's uncomfortable at any age, and if you get it when you're older, if can be really painful. Medical research has shown it can lead to other problems.
That's why experts are calling for kids to be given a jab to stop them suffering in the future.
Kids in America, Canada, Australia and Finland already have the jab.
Researchers from universities in Bristol, London and the Australian city of Sydney and Scottish health experts worked on the report which is calling for the jab.
It followed a study of chickenpox sufferers under the age of 16 who went to hospital because of problems resulting from the illness.