Cockroaches are among the most ancient winged insects, the earliest fossils dating back to about 400 million years. Several conflicting phylogenies for cockroach families, subfamilies, and genera have been proposed in the past. In addition, the relationship of Cryptocercidae to other cockroach families and the relationship between the cockroach, Cryptocercus punctulatus, and the termite, Mastotermes darwiniensis, have generated debate. In this paper, a phylogeny for cockroaches, mantids, and termites based on DNA sequence of the mitochondrial ribosomal RNA genes is presented. The results indicated that cockroaches are a monophyletic group, whose sister group is Mantoidea. The inferred relationship among cockroach families was in agreement with the presently accepted phylogeny. However, there was only partial congruence at the subfamil and the generic levels. The phylogeny inferred here does not support a close relationship between C. punctulatus and M. darwiniensis. The apparent synapomorphies of these two species are likely a manifestation of convergent evolution because there are similarities in biology and habitat.Cockroaches (order: Dictyoptera; suborder: Blattaria) are among the oldest winged insects known, dating back to the Carboniferous (1). About 4000 species of cockroaches have been described (2). A number of conflicting classifications exist for cockroaches, the most widely accepted ofwhich is that of McKittrick (1), based on morphological characters. She considered the order Dictyoptera to include cockroaches, mantids, and termites, each with its own suborder. She divided the suborder Blattaria into two superfamilies, Blaberoidea and Blattoidea, and five families, Polyphagidae, Blattellidae, and Blaberidae (all Blaberoidea), and Blattidae and Cryptocercidae (both Blattoidea). Three other major cockroach classifications, based on morphological characters, have been published during the past four decades (3-5).In addition to the overall phylogenetic relationships among cockroaches, two other issues have generated debate. The first is the relationship of Cryptocercidae to other cockroach families. Cryptocercidae consists of one genus (Cryptocercus) and three species (6) and is generally considered a sister group of Blattidae (1). However, it was recently proposed that Cryptocercidae be merged with Polyphagidae (7). The second issue concerns the relationship among cockroaches, mantids, and termites. Three major schemes have been proposed: Blattaria and Mantoidea are sister groups and Isoptera is a sister group of the Blattaria-Mantoidea complex (8), cockroaches and termites belong to the order Blattodea and mantids are a sister group to that order (9), and all three groups belong to Dictyoptera (1, 10). Of particular interest is the presumed close phylogenetic relationship between Cryptocercus and the termite, Mastotermes darwiniensis. M. darwiniensis has been considered the most archaic living termite species and the "missing link" between cockroaches and termites (11). It is the sole living rep...