When faced with a cat that is peeing outside of the litter box, the first thing many owners think is "bad cat." Stop right there! Pets don’t choose where to urinate maliciously; they pick what will work best for them at any given point in time.
As youngsters, most cats are "hard wired" to pee in a loose substrate like soil, sand, or cat litter. This is why we don’t have to train kittens to use the litter box. Just show them where it is, and they’ll take it from there. But when circumstances change a cat will alter his behavior accordingly.
Illness is the first thing to worry about. Certain medical problems make cats produce more urine than normal (e.g., kidney failure or diabetes mellitus) or have an increased sense of urgency associated with urination (e.g., feline interstitial cystitis, bladder stones, urinary tract infections, etc.). In these cases, a cat may simply think, "Hey, I’ve got to go NOW!" and not take the time or feel well enough to find the nearest litter box.
Therefore, the first thing an owner should do when faced with a cat urinating outside the box is make an appointment with a veterinarian. He or she will perform a physical exam and run a urinalysis. Depending on the findings, other tests like blood work, abdominal X-rays, and an abdominal ultrasound may be in order. Just keep in mind that some of these problems can be easily managed (e.g., with a change in diet) so as tempting as it might be, don’t skip this step.
If your cat has been given a clean bill of health, it is time to move on to the environmental and behavioral causes of inappropriate urination. Cats may develop an aversion to using the litter box for a number of reasons, including
A box that is not cleaned frequently enough. Cats are very fastidious and many will not go into a box that smells bad or that is soiled.
A box that contains a different type of litter from the one the cat is familiar with.
Litter containing a lot of strong perfumes.
A box with high sides, making it difficult for the cat to get in and out of it. This is especially true for disabled, sick, or arthritic cats.
A covered box that is too dark and small, making it uncomfortable for cats to enter and move around inside.
A bad experience associated with the box, like being attacked by a housemate while inside.
Given enough time, a cat that urinates on the rug or other unsuitable surface will start to feel that this is normal behavior. It can be difficult to get these cats to start using cat litter again, so owners need to deal with inappropriate urination as quickly as possible.