This article is from the Feline Leukemia (Cats) FAQ, posted to rec.pets.cats newsgroup. Maintained by Erin Miller with numerous contributions by others.
The mere fact of testing positive is not enough to merit putting a cat to sleep, although there may be other significant factors involved which do make putting the cat to sleep the best option. There are vets who recommend putting all FeLV+ cats to sleep. If your vet recommends this and you feel comfortable with that decision, then that is the best solution. Sometimes putting an FeLV+ cat to sleep is the best option for the cat, especially if it has acute symptoms and is in pain. This is never an easy decision and one which should not be taken lightly. If you do not feel you are capable of emotionally dealing with having an FeLV+ cat (or cannot keep the cat indoors), but do not want to put the cat to sleep, there are other alternatives which are discussed below. The one thing you should not do is ignore the virus. If your cat has tested positive, then you have a responsibility to take some action. FELINE LEUKEMIA VIRUS WILL NOT GO AWAY IF YOU JUST IGNORE IT!