Roundworms are small brown or white worms that are very common in cats. Most cats are infected with them at some time in their lives. Kittens can get them through their mother's milk. Older cats can get them by eating infected mice or other small animals.
Adult roundworms live in a cat's intestines and show up in vomit or feces if the infection is severe. Since roundworms spread easily to other animals and to humans, prevention and treatment are important. Keeping cat litter boxes clean and limiting their opportunities to consume small animals helps. A regular worming program for kittens and adult cats further limits the risk.