Blastocystis sp. is an intestinal protozoa that was formerly recognised as a yeast. However, it has since been classified in the Stramenopile Kingdom. In addition to being observed in humans, the disease has been diagnosed in a wide range of animals (mammals, amphibians, birds, reptiles and arthropods). Extensive genetic heterogeneity has been demonstrated. Blastocystis sp. subtypes 1 to 9 were recently considered to be of zoonotic origin. While some suggested that Blastocystis might play a pathogenic role in intestinal disorders in humans, others reported that there was no correlation. Furthermore, amoeboid forms of Blastocystis might be implicated in pathogenesis. In spite of recent reports, earlier data on the prevalence of the parasite suggest that blastocystosis could have occurred sporadically or continuously in the past. It might be speculated that in cases of zoonotic genotypes producing amoeboid forms, Blastocystis sp. infection might rather be considered a potential re-emerging zoonosis.