|Cryptosporidium species were recognized and named over 80 years ago, these small obligate intracellular protozoans remained until, recently nothing more than a biomedical curiosity. Beginning in 1982, our concept of these protozoan parasites changed, now it is regarded as an important cause of diarrhoea in immunocompetent and immunocompromised subjects. Cryptosporidium spp. are apicomplexan parasites that infect the micro villous border of the gastrointestinal epithelium of a wide range of hosts, including humans. Cryptosporidia have been found most frequently in stools of children aged less than 3 years. Cryptosporidiosis is reported worldwide but its prevalence varies widely in different parts of the world. In the more industrialized countries of North America and Europe, the prevalence rate is 1-3%, while prevalence rates are higher in underdeveloped continents, ranging from approximately 5% in Asia to approximately 10% in Africa. In India, prevalence has been reported to be between 1.3% - 18.9%.Their oocysts are highly infectious, which are transmitted by contaminated water, faecal transmission from infected animals, person-to-person spread or by contaminated food.