Fil: Velásquez, Jorge Néstor. Hospital Municipal de Infecciosas Dr. Francisco Javier Muñiz; Argentina.Fil: Chertcoff, Agustín Víctor. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas; Argentina.Fil: Etchart, Cristina. Hospital Municipal General de Agudos Dr. José María Penna; Argentina.Fil: di Risio, Cecilia. Hospital Municipal General de Agudos Dr. José María Penna; Argentina.Fil: Sodré, Fernando Campos. Universidade Federal Fluminense. Departamento de Patologia. Centro de Ciências Médicas; Brasil.Fil: Cucher, Marcela A. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Carnevale, Silvana. Hospital Municipal General de Agudos Dr. José María Penna; Argentina.Microsporidia are eukaryotic, intracellular obligate parasites that infect invertebrate and vertebrate animals, and have emerged as important opportunistic parasites in AIDS patients. We used light microscopy to detect microsporidial spores in stool samples of a domestic cat confirmed as Encephalitozoon intestinalis by PCR, owned by an AIDS patient with chronic diarrhea and E. intestinalis infection. Cats can be considered hosts of E. intestinalis.