Help - cat for 5 years now running off after getting kitten

You definitely need to keep him in for safety...
How did you introduce the two of them? did you do any kind of slow introduction? Or just brought the kitten into the house and set her loose?

Ok, now I get the picture... We will help you through that... Thanks for answering...
Definitely definitely keep him inside from now on! My goodness! I am so glad you got him "safe"! He probably got into a fight... This episode is showing he is really not fit for the outside...

Since there was a change in behavior, you might want to take him to the vet to see if there is something wrong... He might be sick... You mentioned he is skinny... I do think a vet check is in order to clear things up... Please ask for a blood, urine and fecal test.

Then start with introducing them properly then we go back to keeping him happy inside.
The key is doing a slow introduction. You will need to separate them for a while. There are a couple of articles that will help you tremendously, they can be found here: http://www.thecatsite.com/Behavior/49/Id-like-you-to-Meet...-Introducing-Cats.html and http://www.thecatsite.com/Behavior/49/Id-like-you-to-Meet...-Introducing-Cats/2.html

Take time, and go slowly - this will be crucial for a peaceful relationship in between the two for the rest of their lives...
The reason he is running away is probably that he feels his territory has been invaded - you can try to fix this by doing a proper introduction; it might take a little longer now that he is already stressed out, but it can be done.
I highly recommend Feliway diffusers on the room he spends the most amount of time, and probably on the kittens new room as well (while she is separated. I get mine from Amazon, as it is way cheaper, almost 1/2 price - you can get it here.

Now, to keep him happy inside, you can do several things:

• Assure that he is not bored - have playtime sessions with him, cats LOVE the Da Bird toy, but you can play with just about anything, paper balls, balls, just keep him entertained. Two sessions of 15 minutes a day will do wonders.
• Give them plenty of vertical space - Cats love to watch the world form the top! Window sills are the kitties' versions of our dream home theater; cat trees are great for playing chase, and shelves on the walls are great fun. If you have book shelves, clean up some space and put some folded blankets for them.
  I have a kitty wall that I built in my house with shelves and my cats just LOVE it!

If you give your kitties plenty to do inside, an window sill, and vertical space, chances are they will be just fine inside... I have 3 in my tiny little one bedroom apartment, including an ex-feral kitty and they are very happy together...

Don't feel shy to ask questions, if you need anything at all, we will be here to help you through!

Good luck!

Please also take him to the vet - it is really not a good sign that he has been getting skinny, and the sudden change of behavior can be a sign of trouble. Do not put that possibility out...
I would make that "while" a forever thing by the way...
Good luck!

Carolina, I thought your post was fantastic. Question: the OP's kitten has been with him 2-3 months now. Wouldn't this be long enough to integrate the two cats?

Thank you...
It really depends on the cat's personality... Sometimes the wrong introduction can create lifetime problems. But since it hasn't been too long, I do think he still has the opportunity to try to reverse the situation by doing a slow intro with them... The resident cat needs to feel at ease again, and the hierarchy needs to be established...
I also do think however that it is possible that he might be sick because of the sudden change of behavior, since he was fine with the kitten for a little while and is also losing weight. That's why the recommendation to see the vet.
Re-intros are harder and do take a little longer, but can be done - it is even done when cats have been living together for a long time and start getting aggressive towards one another, or after long vet stays, etc. It works!

Five years ago, we introduced a 7 mo. old to a house with a 9 year old. Our older cat was extremely stressed and she lost weight and probably would've run off had she not been an indoor only kitty. She hid A LOT and she also developed a couple of urinary tract infections, most likely as a result of the stress. We did the intros slowly, but evidently that wasn't slow enough for her! It took her a good 2 years to completely get back to her "normal" self, but it was several MONTHS before the two kitties got along well enough for her to calm down. Feliway helped us tremendously. I still run it 24/7 and can tell when the girls get hissy, it's time to change out to a new bottle.