New kitten and one year old cat

Question
I have a 1-year-old cat named Boo who is an indoor/outdoor cat. I just got an 11 week old kitten and when I brought her home, Boo hissed and took a swipe at her. How do I introduce then to each other so they get along. Also I'm afraid that since Boo goes outside she will run away now that we have a new cat, do you think this should be a concern?

Answer
Taylor,

Boo's reaction is natural and expected.  At this point, since they have already met each other, you may as well let them run together.  You may have to have different litter pans in different parts of the household temporarily.  You may have to have different food dishes temporarily.

Any noise, hissing, spitting, posturing is to be ignored.  If they engage in games of chase, even though it ends up in a "fight", this is a good thing.

Most adult cats are fairly tolerant of young kittens, so they will get along.

I would not let the new kitten out for a few weeks so that it gets the idea that your household is home territory.  Boo will, eventually, show the new kitten the ropes.  Cats are very territorial, and, once they have an established territory, they tend not to roam far from their home base.

One thing you want to do is to show Boo extra affection and give him extra special treats so that he associates the arrival of the new kitten with good things.  Remember, cats do get jealous.

Please let me know how it goes.

Best regards... Norm