Dientamoeba fragilis is a pathogenic trichomonad parasite with a worldwide distribution. It is an emerging cause of gastrointestinal disease in humans with a propensity to cause chronic infections. Although D. fragilis was discovered over a century ago, and is more common than Giardia and Cryptosporidium very little is know about the biology, pathogenesis, life cycle and mode of transmission of this parasite. Recent advances in the understanding of this organism include; new electron microscopy data, sequencing of the D. fragilis transcriptome, the establishment of an animal model using laboratory rodents, fulfilling of Koch's postulates, and the discovery of a new cyst stage in the life cycle of D. fragilis. These new discoveries will be discussed in length.