When I bought my SanDisk Extreme UHS-1 SD card from a local store, it didn't say "Class 10" on it, so I was concerned. I also wasn't sure if it would work in my D5100. Rest assured, after looking online, it is a Class 10 (to the best of my knowledge/research) and does work in the D5100. I just wanted to post that in case anyone else was considering using this card in their camera. It's fast in the camera and in the computer.