We waited until Sadie was about 1 year before we added Cincy to our family and they get along great. My sister and brother-in- law waited til their dog was closer to 3 ( a beagle mix) and got a Malamute mix and they also get along very well. Take your time and really look into the dog, don't go on impulse. When we got Cincy, we took Sadie along and let them meet to make sure there was no immediate personality conflicts. Sadie was not overly thrilled, but within a few days she was watchin out for her little sis and still does 6 months later!