Investigations of elasmobranch anatomy have led to the development of several controversial classifications. Our objective was to deduce the phylogeny of elasmobranchs using molecular data. We extracted DNA from five species representing the major lineages of elasmobranchs and amplified and sequenced a portion of the 12S mitochondrial gene from each extract. The resulting sequences were aligned using the homologous region from a holocephalan as an outgroup and were analyzed phylogenetically. These analyses resulted in a single most parsimonious tree with a length of 121 steps and a consistency index of 0.84. The topology of this tree was unaffected by variable schemes of weighting character transformations. One thousand replications of a bootstrap analysis resulted in a consensus tree with identical topology and with all nodes appearing in at least 71% of the trees. We compared this molecular-based phylogeny with many traditional morphology-based classifications.