Heelys - lots of you may have got them for Christmas.
They look like trainers, but they have wheels in the heels which turn them into skates.
Press Packer Thomas emailed Newsround because he thought that Heelys were dangerous.
And Newsround helped him investigate further.
"I wrote into Newsround because I was worried that Heelys might be dangerous and I wanted them to help me investigate.
First of all I spoke to Isabel, a girl from my school, who fractured her ankle while wearing them.
She had been heelying on a bumpy surface and fell over on her ankle.
She ended up in hospital and had a plaster on for over three weeks.
It was tough for her because she broke her ankle over Christmas and couldn't play with any of the sporty presents that she got.
Charlie from Heelys HQ talks to Thomas about them
I felt really bad about what happened to her and so I went home to do some more research.
Newsround helped me to organise an interview with a man from Heelys, Charlie Allen.
I went down to Bristol to meet him in the Heelys warehouse.
The warehouse was huge and there were loads of Heelys in boxes which were about to be sent out to shops all around the UK.
I asked Charlie whether he thought that Heelys were dangerous.
He said that Heelys recommend that everyone should wear safety equipment and only heel on a flat, dry surface.
He showed me all the safety equipment that you should use - wrist guards, knee pads and helmets.
Lots of warnings
Charlie shows Thomas the safety gear children should wear
I felt better after I spoke to him because I realised that Heelys do put a lot of warnings and safety advice about using Heelys on the packaging.
Next I decided to go and meet my friends in the park to see whether they took any notice of the advice.
Most of my friends don't wear safety gear because they don't think they need to.
By the end of my investigation I felt that Heelys are less dangerous than I first thought.
I found out that Heelys give lots of safety advice but it's up to children to make sure they follow it.
I'm still not sure if I'm going to get a pair though!"
Thomas, 10, Buckinghamshire
If you have had a Heelys accident, tell us about it by clicking on the link on this page.
Why don't you write us a Press Pack report - and get it published on the site?!
It can be about anything that's happened in your local area - or your views on the news.