Toxocara canis (also known as dog roundworm) is worldwide distributed helminth parasite of dogs and other canids. T. canis are gonochorists, adult worms measure from 9 to 18 cm, are yellow-white in color, and occur in the intestine of the definitive host. In adult dogs, the infection is usually asymptomatic. By the contrast, massive invasion of T. canis can be fatal in puppies. As paratenic hosts, a number of various vertebrates, including man, and some invertebrates can become infected. Humans are infected, like other paratenic hosts, by ingestion of embryonated T. canis eggs. The disease caused by migrating T. canis larvae (toxocariasis) results in two syndromes: visceralis larva migrans and ocularis larva migrans.Owing to transmission of the infection from bitches to puppies, preventive anthelmintic treatment of newborn puppies is strongly recommended. Several anthelmintic drugs are effective against adult worms, for example pyrantel, fenbendazole, selamectine etc.