Conservative morphological characters make identification of mullet species difficult. As a consequence, cosmopolitan distribution of Mugil cephalus is currently under discussion. In order to clarify the controversy regarding the taxonomic status of the southern Atlantic American mullet M. platanus, in relation to Mugil cephalus, a comprehensive analysis is presented using sequences of the mitochondrial gene cytochrome b, landmark-based morphometry and meristic data. The interlandmark distances showed differentiation between individuals of M. platanus and M. cephalus analyzed. Variables, representing the height at different levels of the longitudinal axis of the body, exposed that M. platanus has more robust middle and caudal segments of the body, in a lateral view, with respect to M. cephalus. Transversal series scales have not been useful for the identification of species. Lateral series scales seem to be useful to differentiate species, but taking into account that range showed an overlapped gradual variation. Genetic distance obtained between species shows a typical intrageneric level comparison. Two clear phylogroups have been detected indicating a high degree of genetic isolation between both species. Recognition of M. platanus as valid allopatric species is suggested.