There are different reason why cats are not using their litterbox, a medical problem, to be on the safe side and take the cat to the vet and if there is nothing wrong with the cat then their is a behavioural problem and that can be fix. If their are more then one cat in the household then their should be a littlerbox for every cat. Litterboxes should be in a good location, quiet spot where their not alot of traffic. Some cats are fussy about what litter you are using. Make sure the littlerbox is always clean because some cats hate using dirty litterbox. Hope that helps.