I have both covered and uncovered for my brood of 11. The option of both seems to make them happy and I have some that will use both and don't seem to have a preference. I used to only have covered ones. But one of my babies would sit on top and wait for her unsuspecting siblings to come out and then whack whoever a few times on the head. Well, when the some of crew got wise, they started doing the same to her. She got scared and stopped using the covered litter box and would do her business in the house. I had to retrain her to use an uncovered litter box. You know, we gotta and do just love them don't we!!