Microsporidians are primordial eukaryotes with about 700 known species. Lacking mitochondriae, the microsporidiae are intracellular parasites of other eukaryotes, ranging from protozoans to humans. The involvement of Microsporidians in several human pathologies was discovered during the 1950s. However, it was only in the 1980s, with the emergence of AIDS and the use of immunosuppressors during organ transplants, that the association of microsporidians and several opportunistic infections was demonstrated. Since then, several cases of microsporidial infections in non-immunocomprimised patients have been reported.