Dientamoeba fragilis is a protozoan parasite found primarily as a trophozoite in human stool specimens. Its trophozoites measure 5 to 15 micrometers in diameter and most commonly have two nuclei. Less commonly, uninucleate forms are seen. The nuclear chromatin has a characteristic fragmented appearance. The trophozoites have broad, sometimes angular pseudopodia, and the internal flagellum is rarely seen in trichrome-stained preparations.