What kind of worms?

Our Vet explained that you may think you have treated round worms, but they may reappear. Some part of the cycle burrows into the body, and will then come out again even months later. Sort of like the Herpes virus that causes Chicken Pox. Years later it can reappear as shingles.

We use Revolution for the boys, because it can control round worms.

If it is tape worms, cats can get them from fleas and inappropriate eating habits.