ABSTRACT Phylogenetic analyses of cytochrome-b sequence data from 13 of the 15 currently recognized species of New World porcupines were used to test competing taxonomic hypotheses and to explore scenarios of morphological evolution and biogeography. Consistent with previous studies, the monophyly of Erethizontidae (Chaetomys + Erethizon + Coendou) and the monophyly of Erethizontinae (Erethizon + Coendou) were both strongly supported. However, cytochrome- b sequence data provide no support for the reciprocal monophyly of Coendou, “Echinoprocta,” and “Sphiggurus” as those taxa were previously recognized by authors. All of the erethizontid species recognized in recent revisionary work and represented by multiple sequences in this study were recovered as monophyletic groups. Maximum-likelihood (ML) analyses of these data recovered the following phylogeny for 11 species of Coendou: ((melanurus (ichillus (pruinosus + vestitus))) ((spinosus (bicolor + nycthemera)) (prehensilis (mexicanus (quichua + rufescens)))...