Cat not using litter box

Question
My cat keeps pooping right outside her litter box and hasn't done it in her litter box now for probably 1 or 2 months.  I took a stool sample in and it came out negative.  Not sure what to do with her.  Any advice?

Answer
Marie -

You did not say what kind of cat you have, how old she is and how long you have had her.  These questions are important in determining why she is not using her litter box.  

If you will be so kind, please answer the above questions and I will be happy to follow up with you.  

Best Regards,

Charlotte Sherrell, DVM