This review shows the Microsporidia as unicellular protozoa strictly intracellular eukaryotic parasites of animals and humans. These study concerns life cycles, cytology, host-parasite relationships in animal models experimentally infected with microsporidia from human feces, demonstrating the host-inespecificity and visceral dissemination with histopathological studies in digestive, tract, kidney, liver, spleen, brain, heart, pancreas, thyroid, suprarenal glands. It is presented the microsporidiosis in Venezuela in immunocompetent patients and immunodeficients HIV+, with diarrheic syndromes with keratoconjuntivitis microsporidial punctata diffuse and with disseminated microsporidia in urine, tracheobronchial sputum, nasal and pharyngeal exudates. Also we have found the microsporidia in river and lake waters and in animals relationed with the man: dogs, cats, pigs, monkeys, donkeys, guts. The patients are treated specially with Albendazole and also with Trimethoprim-Sulphametoxazol for the children until two years of age. We use as laboratory diagnosis the technique of Kinyoun stain, in support of the acid resistance property of these parasites, and also the Chromotrope staining. Our recommendations for a proper identification of the Microspora species, should be done with Electron Microscopy and the TCR reaction.