Medical causes of house soiling (as urination in the house is known) include bladder infections, prostate problems, hormone imbalances, bladder inflammation and syndromes such as diabetes (in cats and dogs) and kidney disease that cause increased thirst and urine output.
Behavioral house soiling is very frustrating. Stress or anxiety may cause pets to urinate inside the house. Cognitive dysfunction (senility) is a cause of house soiling in older pets. Some pets, especially those that have not been neutered, may urinate indoors as a natural territory marking behavior.
A veterinarian should assess any pet that urinates inappropriately. Blood and urine tests (and, on occasion, X-rays and ultrasound) can check for a medical cause of house soiling. If none is found, then behavior modification may be beneficial.