Despite the increasing number of studies on the systematics of the Stephanoberycoidei (bigscales, pricklefishes, gibberfishes, hispidoberycids, and whalefishes) globally, knowledge about the diversity and distribution of the group in the western South Atlantic still remains fragmentary. In this study, we present new anatomical (meristic and morphometric) and distributional data for 18 species of the Stephanoberycoidei based on the examination of 150 specimens recently collected during the ABRACOS (Acoustics along the BRAzilian COaSt) expeditions off northeastern Brazil, including the Rocas Atoll, Fernando de Noronha Archipelago, and the seamounts off Rio Grande do Norte State, and additional museum specimens. In the Melamphaidae, remarks on the taxonomy of Melamphaes polylepis and of the Poromitra crassiceps and P. megalops species groups are made based on specimens examined. In addition, Scopeloberyx opercularis, currently considered as a junior synonym of Scopeloberyx robustus, is recognized as a valid species. Among the species identified, nine have their distributions extended in the western South Atlantic based on confirmed records: Melamphaes polylepis, M. typhlops, Poromitra megalops, Poromitra sp., Scopeloberyx opercularis, Scopeloberyx opisthopterus, Scopelogadus mizolepis, Cetostoma regani, and Rondeletia loricata. Eight further species are reported for the first time in Brazilian waters: Cetomimus sp. 1, Cetomimus sp. 2, Ditropichthys storeri, Gyrinomimus bruuni, Melamphaes eulepis, M. leprus, M. longivelis, and Melamphaes sp. Additional remarks on the taxonomy and distribution of the Stephanoberycoidei in the western South Atlantic are also provided.