Dendroctonus pseudotsugae Hopkins is a bark beetle that feeds on Pseudotsuga trees. It is distributed from British Columbia to Northern Mexico. Recently, the subspecies D. pseudotsugae barragani was described from specimens collected in Western Sierra Madre in Mexico, being distinct from the nominal subspecies D. pseudotsugae pseudotsugae, which corresponds to populations in United States and Canada. We present a first reassessment of the taxonomic separation of D. pseudotsugae combining morphological and molecular characters (cytochrome oxidase I mtDNA). This study includes specimens from Canada and United States populations while also increasing greatly the geographic representation of Mexican populations. The preliminary results of morphological analysis suggest that intraspecific variation within Mexican populations is greater than previously considered, although at least four of the characters proposed originally for separating the subspecies actually show unambiguous and consistent differences among Mexican and northern populations, while other characters tend to have overlapping variation ranges between populations. Molecular analysis of 50 different haplotypes obtained from 151 COI sequences (550 bp long) supports the existence of two discrete, distinct groups (Mexican and more boreal populations of D. pseudotsugae). Relevance of this study lies both in the potential of D. pseudotsugae as a model for examining the general problem of the existence, definition and delimitation of subspecies, and in the implications of this supposed biological distinctness for the management and conservation of Pseudotsuga stands in Mexico.