All 7 of my kitties are on Revolution, never had a problem with it.

We use it at work on LOTS of cats and I think out of several hundred cats (don't know an exact number) we've only ever had one cat that had some mild hair loss at the application site, and the fur grew back. It's a very safe product that does lots of things for kitties (heartworm, fleas, roundworm, earmites) which is why I use it on my own cats.