Cat going to the bathroom outside of litter box

Every so often my one cat will go to the bathroom (defecates) on my bed.  I am always changing the litter box and cleaning it out.  What could be causing her to do this?  She is approximately 6 years old and this just started within the last 6 months.

[Mrs_Savas]

Hi,

We have a really good article in the Health Pages here on MedHelp that might be useful for you, on cat litter box issues.  I would really recommend it.

Otherwise, take a look at what else has changed in the last 6 months.  If you are sure that your kitty has a clean bill of health, then this behavior is likely caused by something changing in the cat's environment.  Cat's dislike any kind of change and going outside the litter box is usually their way of telling you something!