The South American Trogidae are revised. Three genera, Trox Fabricius, Omorgus Erichson (with two subgenera, Omorgus and Haroldomorgus Scholtz), and Polynoncus Burmeister, and 47 species are recorded from the continent and its islands. Trox is represented by the ubiquitous introduced species T. scaber (L.), Omorgus is represented by 13 species and Polynoncus by 33 species. Five new species are described and all others are re-described. A key to all taxa is provided. Adults of all species and their male genitalia are illustrated and their distributions mapped. Observations are presented on phylogeny, zoogeography and biology. The new species are O. capillaceus, O. indigenus, O. nocheles, P. erugatus and P. gibberosus. Four new synonymies are proposed (synonyms listed first): O. triestinae Pittino = P. suberosus (Fabricius); P. furcifer Pittino = P. bifurcatus (Vaurie); P. parafurcatus occidentalis Pittino and P. furcillifer Pittino = P. parafurcatus Pittino. Omorgus badeni (Harold) is reinstated as a valid...