Two populations of stromateid fishes occur along opposite coasts off southern South America and are recognized as distinct species. The available names are Stromateus brasiliensis Fowler, 1906, for the Atlantic population and Stromateus stellatus Cuvier, 1829, for the Pacific population. These allopatric species can be completely distinguished on the basis of vertebral counts. Differences also exist in median fin-ray numbers, pectoral fin length, head length, and otolith length. The genus Stromateus is described and a key is provided to the three species. The third and quite distinct species, S. fiatola, occurs in the Mediterranean and off West Africa. The two South American species occupy an intermediate systematic position between S. fiatola and Peprilus snyderi, the most primitive species of an advanced stromateid genus.