Neospora caninum is an obligate intracellular protozoan parasite which primarily causes diseases in dogs and cattle all over the world. It was first described in Norway in the mid-eighties in dogs, after which, until the present time, clinical neosporosis was proven in sheep, goats, deer, rhinoceroses, horses, and experimental rodents. Antibodies against N. caninum have been found also in the serum of water buffalo, red and gray foxes, coyotes, camels, and felines. Due to the similarity of this Coccidia with Toxoplasma gondi, the neosporosis was for a series of years incorrectly diagnozed as toxoplasmosis. Domestic canines, dogs, are the only real host for N. caninum. Its life cycle covers three stages of development: tachyzoites, tissue cysts and oocysts. Carnivores are infected by ingesting parts of infected tissue which contain tissue cysts with bradyzoites. The dominant pathway of transmission of this cause in cattle is transplacentary infection, but cattle can also be infected by ingestion of feed or water contaminated by sporulated oo-cysts of N. caninum. Bitches can be subclinical carriers of the parasite, when they pass on the cause transplacentarily, which results in more than one litter being born with the infection. Neosporosis today appears as the main cause of abortions and neonatal deaths in dairy cows and fattening cattle in almost all parts of the world, but with the highest incidence in the United States (US), New Zealand, The Netherlands, and Germany. The treatment of this disease has not been fully determined, but medicines used for the treatment of toxoplasmosis have yielded certain good results. There is no verified vaccine that would prevent undesired abortions in cattle. .