Some 35 species (mostly Neotropical, 22 new) of acalypterate flies representing 17 genera (3 new) in six families, as follows, are treated: Family Cypselosomatidae. One species from Nepal, Cypselosoma gephyrae Hendel (?), is discussed.Family Pseudopomyzidae. The classification of the family is reviewed, and a key to the world genera is provided. The genus Latheticomyia Wheeler is placed here for the first time, and two new species, L. longiterebra (Peru) and L. rotundicornis (Mexico), are described. Two new genera, Pseudopomyzella and Rhinopomyzella, are erected for three new species, P. flava (Peru), R. albimana (Brazil), and R. nigrimana (Brazil).Family Periscelidae. The genus Periscelis Loew is recorded from Mexico and Peru. Neoscutops peruvianus and Scutops striatus, both from Peru, are described as new.Family Aulacigastridae. The classification of the family is reviewed and a key to the world genera is provided. Schizochroa plesiomorphica (Peru), S. minuta (Ecuador), S. ecuadoriensis (Ecuador), Cyamops neotropicus (Peru), C. australicus (Queensland), and Planinasus venezuelensis (Venezuela) are described as new.Family Odiniidae. The classification of the family is reviewed and a key to the subfamilies and the world genera is provided. Two new species of Schildomyia Malloch, S. peruviana (Peru) and S. trinidadensis, are described. A new genus, Shewellia, is erected for the species S. agromyzina (Peru).Family Heleomyzidae. One new species of Cephodapedon Malloch, C. nigriventer (Chile), is described. The genera Mayomyia Malloch and Cinderella Steyskal are reviewed and placed in this family for the first time. Four species of Cinderella, C. macalpinei (Ecuador), C. pollinosa (Chile), C. hirsuta (Chile), and C. steyskali are described as new.The paper is accompanied by 72 illustrations.