microsporidia is a common term that has been used to refer to a group of eukaryotic, obligate intracellular protozoan parasites belonging to the phylum microspora. they are important agricultural parasites, contaminating commercial insects; they are also important by infecting laboratory rodents, rabbits and primates. ever since the early cases found by magarino torres, who reported the presence of encephalitozoon in a patient suffering of a meningoencephalomyelitis, some human pathology caused by microsporidia has been described. however, only after the acquired immunodeficiency syndrome outbreak have these organisms appeared as significant etiological agents in different pathologies. even so, they remain underestimated. in the present article, the importance of microsporidia for the human pathology in immunocompromised host has been stressed.