Which parasites can be transmitted by household cats and dogs? Certainly a variety of potentially dangerous helminths and protozoa can be transmitted to humans from pets but, for the most part, very special conditions must be present before this occurs. Small children, pregnant women and immunocompromised persons are three groups at greater potential risk than the general population. Infants and toddlers may contract visceral or cutaneous larva migrans, tapeworm infections and, rarely, other helminths or protozoa. Pregnant women and their offspring are at special risk for toxoplasmosis. Immunocompromised persons (including those with acquired immunodeficiency syndrome) are susceptible to multiple infections but especially to cryptosporidiosis, an underdiagnosed zoonosis present in contaminated water supplies. Other zoonotic infections (Echinococcosis, Dirofilariasis) rarely appear in the general population but, when they do occur, pose very real diagnostic challenges. The risk of disease transmission from pets can be minimized by taking a few simple precautions such as avoiding fecal-oral contact, not emptying the cat's litterbox if pregnant, washing hands carefully after handling pets, worming pets regularly and supervising toddler-pet interactions. In most cases, the psychologic benefits of pet ownership appear to outweigh the reducible risks of disease transmission.