There are some highly effective treatments which will kill worms. These are available as liquids, tablets or injections. However, not all the products are equally good and some work against certain types of worms and not others. Your vet will be able to advise you on which product is best for your cat. Worms are so common that it is safe to assume that all kittens, cat with fleas, and animals which regularly catch wildlife will be infected. Kittens should be treated with wormers every two weeks from four weeks to 16 weeks of age and older cats should be treated about every three months. Some cats, eg hunting cats, will need more regular treatment than others. You should discuss with your vet the most appropriate treatment regime for your pet.