It really has a lot to do with personalities....Donna, our meetup co-ordinator has 3 boxers, 2 males & 1 female, they all get along great, oh sure I would imagine there are a few scrapes, but that happena even with just m/f combo....The main reason I am holding out for a puppy is due to Samson and his strong Alpha personality, he could not tolerate another male adult in his house, a pup is another matter....Like Barb said, even rescues are more willing to place a male in a house that already has a male, so it's not the issue as it can be with 2 females....Bottom line, know your dog, is he dominant, submissive? That will be the factor.....