Number of litter boxes - Suddenly having less litter boxes can be a stressor. We recommend one for each cat, in separate locations, plus one extra. For two cats we would recommend three litter boxes in three different locations.
Location of litter box - Try putting the litter box back in its old location with a new one in the new location. If the cat resumes using the box in the old location, place some of the soiled litter from the old box in the new box and your cat may figure out what you want.
Size of litter box - The size of the litter box, especially the height of the sides, can be a big deal to a cat especially if it is suddenly more difficult to get in or out. If you have a large cat, you need a large litter box that will contain your cat comfortably. Often times litter boxes are too small.
Type of litter box - Some cats prefer the traditional open litter box while some prefer the privacy offer by a covered litter box. While the automatic cleaning litter boxes are a great convenience for us, the noises and motions they make when operating can be scary to some cats and can cause them to stop using the box.
Equipment and objects next to the litter box - Most of us like to put the litter box in a secluded location out of major household traffic patterns. This is a good choice for the cat as well unless the box is next to some piece of equipment that has the potential to make noise or move when they are using the litter box. A clothes dryer may normally be okay but when unbalanced it can make louder and different noises. A malfunctioning furnace in need of a cleaning can also be startling when it kicks in. If the cat is scared once, they may abandon use of the box in this location.
Depth of litter in the litter box - Sometimes we humans like to load up the box with litter thinking we'll need to change it less often. Many cats will stop using the box if there is too much litter or too little litter.
Frequency with which the litter box is cleaned - Many cats will not use a dirty litter box and their definition of dirty may be different than ours. We recommend scooping at least once a day and changing all litter and washing the box weekly. Very few cats object to a litter box that is too clean.
Chemicals used to clean the litter box - Cats are very sensitive to odors, so when washing your litter box do not use a strong smelling cleaner and make sure that you rinse it thoroughly.
Litter used (Brand, Material, and Scent) - Cat litter comes in a wide variety of substrates (non-clumping, clumping, sand, wood chips, corn cobs, newspaper, scented, unscented, etc.). Not all cats are going to like all types of litter no matter how much we like them. If you had something that worked before, switch back. Many cats are especially sensitive to some of the scented litters.
Cats are very particular about their elimination area. If you have changed anything in the above list prior to the start of this problem, change back and see if the problem resolves. If you have not made any of these changes try cleaning the litter box more frequently.
Changes in diet can also cause changes in elimination habits especially if the new food is causing some digestive upset. If you have recently changed foods, try changing back and see if that helps.
Changes in medications - If your cat has recently been put on medications or has had a change in the dosage of an existing medication, ask your veterinarian if this could have any effect on elimination habits.
Household changes - The domestic cat is a social species and usually bonds closely with those in its immediate household. The loss of a family member or another pet can trigger depression and grief which can sometimes be enough of a stressor to cause a change in eating, elimination and sleeping habits. Likewise the addition of a new family member, human or animal can also be a stressor. If the elimination problem has started after the addition of a new cat or dog, you will want to work with an animal behavior consultant to assist you in assessing and changing the relationship between the two pets. It is not unheard of for one cat to guard access to the litter box by the other cat. This doesn't necessarily mean they will fight. It might be as simple as one cat lying at the top of the basement stairs which will prevent the other cat from going downstairs.A pet behavior consultant can often help restore harmony to your pet family; however, be advised that this does not always work out. Occasionally one needs to make a choice of living with a problem or re-homing one of the pets. Cats are also very sensitive to everything in their environment and sometimes moving furniture around, changing access to certain rooms or adding or removing furnishings can be a stressor. Changes outside of the home - If our cat is an "indoor only" cat we tend to believe that they are only concerned about their immediate environment - what's inside the house. That is not the case. Cats can be very territorial and a new cat or dog in the neighborhood, especially one frequently hanging around your home, can be a stressor. Cats mark their territory with both urine and feces, so inappropriate elimination may be caused by territorial concerns. When marking territory with feces it is usually left uncovered so it is obvious to other cats in the area. Urinating as a territorial response occurs in two forms; 1) spraying and 2) marking. Spraying typically involves backing up to a vertical surface and spraying urine. Spraying is a very overt act by a confident cat that wants to be seen. Marking involves small drops of urine on a horizontal surface and is usually the result of a non-confident cat that does not want to be observed. Vertical scratching is also a very overt behavior used to mark territory and when combined with spraying and feces marking definitely suggests a territorial component to the cats' inappropriate elimination. Other changes in your neighborhood may also be stressors for a cat. New neighbors, noisy rambunctious children, a raccoon family visiting the yard, or a construction project can all be possible triggers for inappropriate elimination.