Why did my cat stop using the litter box?

How often do you clean your litter box? Some cats won't use the litter box if its not kept up properlly. One way to know if this is the case, is to go out and get freash litter. Dump the old litter, and literally wash out the litter box. Liquid lysal is good, or soap and water will also do the trick. Let it dry completely, then coat the bottem with a layer of baking soda. Then poor about half the contents of the litter into the box, and make sure its even. Almost like spreading cake or brownie mix into a baking pan. Then put your cat in the litter box and pet them, gentely telling them its okay to go. Then leave the cat alone. If the litter wasn't clean enough, then the cat will start using it again. If not, then there is another problem. But, just because an animal refuses to use its litter box doesn't nessarlly mean that its seriously ill.