T. canis is a cosmopolitan parasite. The infection rate in the 50 million dogs inhabitingthe United States is very high; over 80% of puppies and 20% of older animals are in-volved. “Man’s best friend” deposits more than 3500 tons of feces daily in the streets, yards, and parks of America, and there is a real health risk. In some areas, between 10 and 30% of soil samples taken from public parks have contained viable Toxocara eggs. Moreover, serologic surveys of humans indicate that approximately 4 to 20% of the pop-ulation has ingested these eggs at some time. The incidence of infection appears to be higher in the southeastern sections of the United States; presumably the warm, humid climate prolongs survival of the eggs, thereby increasing exposure. Indeed, seropreva-lence rates of more than 50% have been noted in some developing nations. The presence of puppies in the home increases the risk of infection. Clinical manifestations occur predominantly among children 1 to 6 years of age; many have a history of geophagia, suggesting that disease transmission results from direct ingestion of eggs in the soil. Most infections are subclinical, but the incidence of overt disease, although difficult to assess, is certainly underreported. Serious ocular infection by larvae is frequently seen by ophthalmologists.