Causes for this frustrating problem fall into two categories: medical problems and behavioral problems.

Common Medical Causes of House Soiling

More common causes are listed first; less common causes are listed later.

• Bladder infections are by far the most common cause of urinating outside of the litter box.
• Inflammation of the bladder, known as FUS or FLUTD, may cause inappropriate urination.
• Any disease that causes increased consumption of water, such as diabetes mellitus, kidney disease, or hyperthyroidism may cause cats to urinate outside of the litter box.
• Cats with arthritis or mobility disorders may have difficulty reaching the litter box, especially if long distances or stairs must be navigated each time the cat needs to urinate.
• Constipated cats may urinate outside of the box because of excessive straining during attempts to defecate.
• Exposure to certain toxins (especially pesticides) may cause urination inside the house.
• Cats may involuntarily urinate during seizures.
• Irritation of or trauma to the external genitalia very rarely causes house soiling.
• Neurological irregularities may cause house soiling.

Common Behavioral Causes of House Soiling

• Stress is the most common behavioral trigger for house soiling.
• Many cats will urinate outside of the litter box in response to the box not being kept adequately clean.
• Cats may refuse to use a litter box in which they do not feel safe.
• Cats may refuse to use a litter box that lacks privacy.
• Cats in the house may urinate in any area that has previously been soiled, due to the odor of urine in that location.
• Elderly cats may suffer from cognitive dysfunction (senility), leading to a lapse in litter box habits.
• Urinating outside of the litter box occurs as normal marking behavior in some cats. This is especially common in male cats that have not been neutered.
• Cats may be reluctant to use litter boxes that do not provide adequate privacy.
• A cat may refuse to use a litter box if it has been ambushed or attacked by another cat in the house while previously in the box.

Recommended Course of Action

It is critical to determine whether a medical condition is contributing to the inappropriate urination. For that reason, any cat who consistently urinates outside of the box should be assessed by a veterinarian.

Consider neutering or spaying intact cats who urinate outside of the box.

Male cats that urinate outside of the litter box may develop a life-threatening syndrome known as urinary obstruction. Any male cat that demonstrates urinary irregularities should receive immediate veterinary care.

If a veterinarian can find no medical cause for house soiling, implement a behavior modification protocol. More information on this topic can be found in the article entitled Behavioral Modification for Urinating Outside of the Litter Box.

The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.

Dr. Eric Barchas, DVM, is a veterinarian who lives and works in San Francisco. His emphasis is on small animal medicine, surgery and wellness. An avid traveler, he has studied lions in Botswana and salmon in southern Chile.

Dr. Barchas is the resident veterinarian of Dogster and Catster. Since May of 2005, he has provided insightful and thoughtful answers to questions from members. His professional advice has added greatly to the wealth of pet health information on Dogster.com and Catster.com from which this column often comes.