i have 4 cats and they are indoor cats, i have lots of toys scratch posts etc for them and they all play together, my only prob few years ago is when i took in an outdoor cat for someone and it was forever trying to escape out of window [i live on second floor] which wasnt safe so i had to rehome her but other than that no prob at all they are happy safe dont get illness or mishaps in the sameway as they dont come into contact with ther cats and traffic etc