I haven't had two of the same sex in these little guys. I have a boy (biewer)Bogie and a girl (yorkie)Jada. They get along extremely well. Oh and on the potty training note: Jada is the older of my two and I had her before we got Bogie, she was still having accidents about 3-4 times a week. She has done so much better since, I think they compete to see who can pee and poop on the pad first.LOL