Health

• According to "Cat Owner's Home Veterinary Handbook" (Delbert G. Carlson, DVM, et al, 1995), many health problems such as urinary infections or neurological problems can have a cat loose control of its bladder or bowels. A cat that does not use the litter box should be taken to the vet.
  
  

Stress

• Another reason a cat may suddenly stop using the litter box is stress, so that the cat does not feel safe using the litter box. Try moving the litter box to where the cat is hiding or is now going.
  
  

Changes

• Cats have individual preferences when it comes to the type of litter they like. Try changing the type of litter and cleaning the litter box more frequently to see if that makes a difference.
  
  

Hair

• Cats with long hair may get feces trapped in the hair and accidentally drag the feces throughout the home. These cats need trimming under the tail.
  
  

Spraying

• Fully intact male cats spray urine to mark territory, while unspayed female cats will spray when they are in heat. Neutering or spaying should solve the problem.