I have 2 kitties - Otie and Mir and have been thinking of adding another kitten. I am glad to hear from reading the responses that usually they get used to each other. I would like to add to the family, but am nervous about upsetting the balance. Otie is very laid back and accepting. He is 5. Mir is 3 and not laid back at all. She tends to be on the aggressive side with everyone except for her immediately family. My vet has recommended only adding a kitten as opposed to an adult cat. She thinks Mir might feel less threatened by a kitten.