i do mine about every 6-8 wheeks, it depends really.you shouldn't do it more than that really, unless they are really dirty! and as others have said, if it's just a dirty bottom, then just bath that. i trim round the hindquarters so it doesn't get mucky and tangled, and that helps. i brush everyday, wheather they like it or not! this, i find, keeps the hair in good condition O0