The Nearctic leafhopper genus Errhomus Oman (Hemiptera: Cicadellidae) exhibits high host-plant selectivity and female brachyptery, which may limit gene flow. Two subgenera, Errhomus (Errhomus) and Errhomus (Erronus), are recognized based on morphological and behavioral differences. We used mitochondrial DNA sequencing to elucidate the phylogenetic relationships among members of the subgenus Errhomus (Erronus). Portions of the NADH dehydrogenase subunit 1 (ND1) and the leucine (CUN) transfer RNA (tRNA-Leu) genes were sequenced and were analyzed with parsimony and maximum likelihood. Our results generally verified the findings of Hamilton and Zack (1999); however, both optimality criteria revealed a paraphyletic Errhomus (Erronus). Errhomus (Erronus) calvus does not seem to be a member of the subgenus Errhomus (Erronus) but seems to be more closely aligned with the subgenus Errhomus (Errhomus). We tested two a priori null hypotheses: 1) that the phylogeny estimated from the molecular data matched a previous phylogeny based on morphology and biogeography from Hamilton and Zack (1999) and 2) that diagnostic characters of the male genitalia (serrated aedeagal processes and triangular aedeagal shaft tip) were synapomorphies that defined major clades. We rejected these hypotheses with both Bayesian tests and parametric bootstraps.