Litter Box Problems
Many cats occasionally eliminate outside the litter box. Any change in your cat's toilet habits is cause for concern and may signal a health problem. Pain when voiding, for instance, may give your cat an aversion to the litter box. Visit the vet as soon as possible to determine if an underlying illness is to blame.
Assuming the vet gives your cat a clean bill of health, start looking for other causes of his behavior. Is the litter box dirty? Cats have a much stronger sense of smell than humans and will tend to avoid an area where they can smell buried waste, be it their own or another cat's. Remove the waste at least once or twice day and empty and wash the box frequently litter-pan liners can make this job easier. Have you changed the type of litter? Your cat may be averse to the consistency or fragrance of a new brand. Many cats dislike scented litter or litters composed of hard pellets. It's usually best to stick with unscented litter of the type your cat is used to; if you must switch, do it gradually. Where is the litter box situated? If the box is located in a noisy or busy area or if your cat was frightened by something while using it, move it to a safe cat-friendly site. Leave a bowl of dry food at sites where you want your cat to stop eliminating; as a rule, cats dont eliminate at spots where they eat. You may need to move the litter box to its final location gradually or enclose your cat in the room where it is kept until he begins to use it again.
Another possibility is that your cat is spraying urine outside the box. Your cat will stand, tail raised high and quivering, and back paws often stepping rhythmically. Such behavior is usually sex-related, so if your cat, male or female, isnt already sterilized, have it done at once. If you catch your cat in the act, a scolding, "No!" may stop it that one time, but wont solve the problem. In fact, it may compound things by stressing the cat.
If you have recently adopted another cat or a dog, or if a newcomer has joined the household, even just temporarily, your cat may be reasserting its territoriality. Properly reintroduce the cat to the new pet and try assigning a different member of the household to feed and play with each animal.