Phylogenetic relationships between seven elephantfish species from five genera (Mormyridae) that are endemic to southern Africa, and the Nile knifefish of the sister family, Gymnarchidae, were determined using biochemical genetic data, behaviour (the waveforms of the electric organ discharge), morphology, and habitat and food preferences. The results confirmed the existence of an undescribed species of Hippopotamyrus, and that H. ansorgii and H. discorhynchus are not congeners. These distinctions had been suggested by differences in electric organ discharge waveforms and are here substantiated by morphological and genetic data. We recommend the reinstatement of Cyphomyrus discorhynchus (Peters, 1852). Genetic distance (D, Nei, 1972) values suggest confamilial genera (D average of 1.09 for all species studied, and 0.715 for southern African species), with the exception of the sympatric and congeneric species: H. ansorgii and H. sp. (D=0.423). Phylogenies based on morphological and electrophoretic data are congruent.