cat

Hi Catman, things that cause bleeding from the hind end could be an injury, a heat cycle, or smaller amounts of bleeding could be coming from a urinary tract infection or bloody stool from an intestinal problem or worms.  If the amount is significant it would be best to get your cat to the vet as soon as possible as she could become anemic very quickly.  If you cannot get your cat right in, you could call the vet and give them all the information on your cat and see what they might recommend over the phone.  Good luck!