Fil: Velásquez, Jorge N. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Di Risio, Cecilia. Hospital Municipal General de Agudos "Dr José María Penna"; Argentina.Fil: Etchart, Cristina B. Hospital Municipal General de Agudos "Dr José María Penna"; Argentina.Fil: Chertcoff, Agustín V. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Virología. Servicio de Microscopía electrónica; Argentina.Fil: Mendez, Nora.Sector Ecografía de la División Radiodiagnóstico, Hospital de Infecciosas Francisco J. Muñiz, Buenos Aires; Argentina.Fil: Cabrera, Marta G. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Labbé, Jorge H. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Fil: Carnevale, Silvana. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Parasitología; Argentina.Sarcocystis sp is a tissue coccidian parasite in humans that causes intestinal and muscular sarcocystosis in immunocompetent patients. Intestinal sarcocystosis can be diagnosed at the tissue level in the lamina propria of the small bowel and by fecal examination. Muscular sarcocystosis is diagnosed by microscopic examination of muscle biopsies. This report describes a case of systemic sarcocystosis in an HIV-infected patient. We studied a 31-year-old patient with AIDS, chronic diarrhea, cholestatic hepatitis, and musculoskeletal pain by stool analysis and endoscopy with duodenal and liver biopsy specimens that were processed for routine histology. The microgamete and macrogamete stages of Sarcocystis sp were present in the lamina propria, with sporulated oocysts in feces. Schizont stages of the protozoa were found in liver biopsy. In summary, sarcocystosis should be considered another opportunistic infection in HIV-infected patients.