Removing Cat Pee: Why cats go outside the litterbox

There are four reasons that your cat might not be using the litterbox:

The litter box is dirty. Just like we don't relish using a port-a-potty, cats won;t use a litterbox that isn't clean. Fresh litter and a well scrubbed box (not with smelly cleanser mind you) are the first thing to try when the cats start having accidents. Also try a new litterbox altogether - the porus plastics used for most litterboxes can hold smells even after many washings.
Medical Issues - if your cat is not using the litterbox all the time, you should get it checked out by a vet in case the problem can be easily solved (like an urinary tract infection). Especially if your cat has blood in the urine, a small, very hard stools, or loose BMs you should get it checked out.
Territorial Marking - is unfortunatley natural in both male and female cats. A cat will behave very differently when spraying than if they are just peeing outside the litterbox. A cat that is spraying will not turn and sniff or paw at the area when they are done - they’ll just walk away. If you have more than one cat, make sure you have at least one more litter box than the number of cats you have so each can have their own "turf".
Stress - a new pet (or even a new family member), change in litter, even rapid changes in temperature can stress your cats out, and a stressed cat is much less likely to use the box. Using Feliway Spray can help reduce your pets' stress and resume normal bathroom habits.