Teratopactus Heller (Entiminae : Naupactini) is a broad-nosed weevil genus widespread in South America. This first taxonomic revision of the genus includes seven species: T. capucinus (Perty) (type species; syn. T. senex (Boheman)); T. elegans (Lucas), comb.nov.; T. gibbicollis (Boheman); T. nodicollis (Boheman) (syn. T. angulicollis (Lucas), T. paulanus (Fonseca & Autuori), T. serripes (Boheman), and T. perpastus (Boheman), syn. nov.); T. retusus (Boheman); T. tuberculatus (Arrow); and T. vittatus (Mannerheim), comb.nov. All species except T. tuberculatus have a strong ovipositor lacking styli, T. elegans, T. nodicollis and T. vittatus show well developed humeri bearing a strong tooth and T. retusus, T. capucinus and T. gibbicollis are characterised by a strongly gibbous pronotum and reduced humeri. Teratopactus nodicollis is the most variable and widespread species (Argentina, Brazil, Bolivia, Paraguay and Uruguay), T. tuberculatus and T. elegans range through Brazil and Paraguay and the remaining species are endemic to Brazil. The first cladistic analysis of the genus Teratopactus plus two outgroups, using 36 morphological characters, established synapomorphies and revealed relationships between the species in a single cladogram with the following topology: (T. tuberculatus ((T. elegans (T. nodicollis– T. vittatus)) (T. retusus (T. capucinus–T. gibbicollis)))).