Quad bikes can be fun but they can also be dangerous, and people are being told to think carefully before buying them as Christmas presents.
About 1,000 people a year are hurt in quad bike accidents, although experts say they are safe if used properly.
But campaigners are worried that people are buying the bikes off the internet and from car boot sales, and are not getting the proper safety advice.
There are also calls for a new law to make people wear helmets on the bikes.
At the moment, there is no law to say people have to wear a helmet when they're riding a quad bike, although the government does encourage people to.
Last year about 12,000 were sold through bike dealers, who give people free training.
Quad bike riders should have training
Richard Leonard, from Honda UK, said: "These are not a toy, they are designed for work on the land and if used properly they are quite safe."
Peter Cornell, of the Royal Society for the Prevention of Accidents, said he's worried about people who don't buy them from proper dealers.
He said: "If people are buying these off the internet, not from a proper dealership, they are not going to get the safety advice that they need to get."