TAXONOMIC classification is a primary determinant of manage-ment priorities for endangered species. Neglect of distinct taxa may lead to their extinction, a problem exemplified by management of the New Zealand tuatara, Sphenodon, the only surviving genus of one order of reptiles. The pattern of genetic and morphological differentiation reported here supports a taxonomy dating from 1877 that identified two extant species, one subsequently separated into two subspecies. Tuatara were fully protected in 1895, but legislation and assessments of conservation status never acknow-ledged taxonomic differentiation, referring only to Sphenodon punctatus. Perceived monotypy of tuatara apparently forestalled management intervention on behalf of threatened populations, thus contributing to extinction of 10 of the 40 populations (25%) in the past century and the imminent extinction of four more. Iden-tification of diversity within tuatara warrants increased conserva-tion attention for the single populations of S. guntheri (here reinstated as a second living species) and the possibly extinct subspecies 5. p. reischeki.