Cats spray (urinate straight back on a vertical surface, usually with tail held high and quivering) to mark new territory, to let other cats know they’ve been there, and to give an area its own special smell. Intact male cats tend to spray more than neutered males, and both more than female cats. Spraying is normal feline behavior – it’s one of the ways they communicate.

Most pet cats are neutered and generally do not spray indoors. But when they do, it is usually a sign that they are feeling stressed or threatened by something such as a new cat, baby, or person in the house, or a change of routine.

After ruling out a medical cause, such as cystitis (inflammation of the bladder), and making sure what you’re seeing and smelling is on a vertical surface rather than the floor you can probably safely assume that your cat is spraying, and not just urinating outside the litter box. If that is not the case, some behavior modification may be in order.

Do not hit or yell at your cat when he sprays. It will only make the problem worse. Instead, try to figure out why he is feeling insecure and take steps to ease the disruption. If you identify the problem or remove the source, try limiting the area he can roam in your house to improve his feeling of security.

As you work to resolve the problem, remain in consultation with your veterinarian. He or she will guide you through the process, and may recommend medication or refer you to a specialist in feline behavior.

Reference: Cornell Feline Health Center