The most difficult part of solving litter box avoidance problems is identifying the cause. Unfortunately, cats are extremely sensitive to change - and if your cat has been regularly using the litter box and then suddenly stopped, something has changed whether you are aware of it or not.

So the goal is to figure out what's changed.

Here are a couple of things to think about:

The most important thing to consider when you need to figure out what has caused a house soiling problem is: WHEN did the problem start?

2nd most important: Are you certain it's not a health issue such as an Urinary Tract Infection? (The #1 symptom of an UTI is litter box avoidance)

Other questions to consider that will help you figure out the cause:

Did anything at all change near the time when the behavior started? (Try to think of everything, no matter how unimportant it seems)

Have you moved to a new home recently?

Did you recently introduce a new cat/dog/ferret/roommate into your house (or apartment)?

Have any of the litter boxes been moved? (Maybe he or she tends to regularly use one certain box and that particular one has been moved)

Did you rearrange or add any new furniture to your house?

Are you 100% sure this cat is the one not using the box?

Are any of your cats not getting along?

Inter-cat disagreements are actually much harder to spot than most owners realize. Just because they aren't fighting doesn't mean they're getting along. One of your cat's may actually be "silently" intimidating one of the others, but you don't know how to read the signs so you aren't aware of it.

If you're sure you know which cat isn't using the litter box, and you know which litter box that cat usually uses, keep an eye out to see if any of your other cats are spending extra time "hanging out" close to that box.

If you have any covered litter boxes, pay special notice to any cats that have a tendency to sit on top of the litter box.

One surefire method of retraining a stubborn cat is to keep the cat in a nearly empty room for a day or two, providing only a few toys, a scratching post, water, a bed and a litter box.

Use this technique to house train your cat and don't allow free access to the rest of the house until the cat is completely retrained and no longer eliminates outside of the litter box.

Some people think it's crazy when they realize just how many things can upset a cat's bathroom habits. What they don't realize is that elimination is actually a very complex and fragile part of a cat's life, and it can be easily disrupted.