My cat is peeing in the house recently

I've have my cat Pebbles since he was a kitten and I never had a problem with him going in the house but recently he's been doing that instead of going out into the room with the litter box. The people I live with have cat's also and one of their male cat's starded spraying when this new cat came around, that started about a year ago. So now recently Pebbles been going in the house. I know that he isnt spraying, he's just going like he would in his litter box.
Why is he doing this now though after years of not doing this and what on earth can I do about it?

[Aleda M Cheng, D.V.M., C.V.A]

Most of the time inappropriate urination by cats is due to urologic disease such as: urinary tract infection, feline urological syndrome, interstitial nephritis and others.

Please bring your cat and a urine sample (if possible) to your vet ASAP to rule out these physical/infectious causes.

Behavioral inappropriate urination is less common and much more difficult to treat.  It can result from something simple such as changing the kitty litter to something the cat does not like, or, to changing the location of the litter box, or,  not having enough litter boxes for the number of cats in the household.  There should be at least one litter-box more than the number of cats in the house.  If you have 6 cats there should be 7 litter boxes, and a litter box should be on every floor of a house that a cat has access to.


The problem could also be very complex and pertain to the behavioral dynamics and social order in a multi-cat household.  Solving this problem requires being a medical detective at times.   Monitor your cat as often as possible.  Is there a cat bully in the household that pounces on your cat when he tries to use the litter box?  Or is there something much more subtle going on.  

Please take your cat to the vet.  If the problem is purely behavioral please post to us again with additional information and we will try to help.