I went through the same thing last year when we brought a puppy home to live with us and our 4 year old cat. He had been an "only child" for a couple years, so he knew he ruled the roost. The timing working out well for us though- we were also moving into our first house at the time, so when we moved in, noone had established territories- it was new to both of them. At first, Jinx stayed up on the counters and anywhere else the dog couldn't reach him at and avoided him at all costs. When there was a confrontation then and still now, Jinx bops Kody in the nose, and the dog backs off. Jinx still rules the roost, but now, almost a year later, the two of them do get along and can lay in the same room without picking on each other. They play together sometimes- you'll see one chase the other through the house, then they turn around and the second one chases the first one. It's really cute. But all I can say is it depends on the cat, and usually gets better in time. Jinx is very laid back and calm- I think that's why he was able to accept Kody. We're bringing a second Golden into our family the week after next, so hopefully he accepts that too. But I don't anticipate problems- kitty can hold his own against the big pansies. :-)