My cat is not using the litter box reliably. What should I do?
First, address the problem promptly. The longer the behavior persists, the more likely it is to become habit. If you have more than one cat, you may need to separate them until you can identify the responsible party. Alternatively, your veterinarian can provide you with a special non-toxic stain given by mouth that will show up in the urine. In cases of defecation outside the box, you can feed one cat small pieces (about twice the size of a sesame seed) of a brightly colored non-toxic child's crayon that will show up in the feces. If you find urine puddles in the house, it is important to distinguish between spraying and other forms of house soiling. Watch your cat for signs of spraying—or set up a video camera when you're not around.

Once you have identified the house-soiling cat, it is wise to take him to your veterinarian for a thorough physical examination and appropriate diagnostic tests to see if there are underlying medical problems. Cats with medical conditions may not always act sick. Once medical causes have been ruled out, your detective work begins. Here are some patterns that may point to a cause:

• Is there one type of surface upon which your cat eliminates? If so, she may have a preference for certain surfaces, and you can modify your litter to match it. If she likes soft surfaces like carpeting, buy a softer, finer litter, and put a carpet remnant in her box. If she has a penchant for smooth, shiny surfaces, consider putting tiles in her box, covered with only a small amount of litter. Over time more litter can be added.
• Is there a certain location she prefers? She may have developed a preference for a new area because something bothered her about the old area. Try placing a litter box in her "preferred" location. Once she reliably uses it, gradually move the box just a few inches a day back to the desired location. Stop moving the box if she stops using it; instead simply move it back to the spot where she last reliably used it, then gradually begin moving it again.
• Is yours a multi-pet household where another animal terrorizes your cat while she's in the litter box or as she exits? If so, the cat may be afraid to use the box. If you currently use a covered box, replace it with one that gives her a 360-degree view. This will give her more confidence while she's in the box and make her less prone to ambush. Also, position the box so that she has more than one way out (i.e. don't have the box surrounded on three sides). Finally, place multiple boxes in multiple locations to give your cat more options.
• When your cat uses the box, does he cry, refuse to bury his waste, perch on the edge of the box without touching the litter, or eliminate right near the box?
• If so, first be sure the box is clean. Some cats refuse to use a box containing any urine or feces whatsoever; meticulous litter box cleanliness is necessary for these individuals. (See "Keeping the Litter Box Clean.")
• Your cat may dislike the litter you use, especially if you've recently and suddenly changed brands. If you must switch brands, do so gradually, adding more of the new litter to the old with each cleaning. Most cats prefer their litter unscented, and an inch or two deep.

The box itself may be the offender. Larger cats need bigger boxes, and kittens and elderly cats need boxes with low sides. Although humans like covered boxes for reducing odor and stray litter, from your cat's point of view, covers hold odors in, and restrict his view of the area. You may need to purchase several types of boxes and several types of litter to determine which combination your cat likes best. Finally, provide as many boxes as there are cats in the house—plus one. For example, if you have two cats, there should be three litter boxes. This decreases competition and gives each cat a box of his or her own.