The ink is identical, there may be a few more colors of sketch, but the most important difference is that the sketch are refillable, the ciao are not. go to
www.copicmarker.com. They have a good feature listing or search copic here and you will find more info than you need! The sketch are also slightly smaller in diameter and fit better in my hand. I bought a few ciao before I knew the differences and have only bought sketch since. HTH~