Usually by the time you get an adult cat, he's already been housebroken and will even prefer to use the litter box. However some cats have never been trained to use a box or rebel against it for whatever reason. Litter training an adult cat has its own particular set of difficulties, as does any type of training you attempt with an adult cat. As they get older, cats get very set in their ways just like humans do and of course it's difficult to break them of any bad habit or to train them for a good one. If you're attempting litter training an adult cat you may be thinking that it's impossible, but it really isn't if you keep a few simple things in mind.