Analysis of 28 morphological characters supports the existence of two karyotypically defined species of Peromyscus on Vancouver Island and islands in the Queen Charlotte Strait and the Strait of Georgia. Morphology of insular and mainland populations from Washington and British Columbia is congruent with karyotypic data indicating that only the smaller, low fundamental number deer mice should be retained with Peromyscus maniculatus, and that the larger, high fundamental number forms should be referred to Peromyscus areas. Accordingly, P. maniculatus ranges throughout Vancouver Island, is the only deer mouse inhabiting the islands of the Strait of Georgia, and occurs on some of the more northern small islands. Insular forms of P. areas occur on northern and western Vancouver Island and on the islands in the Queen Charlotte Strait. The existence of two species in this geographic area indicates the need for a revision of the subspecific taxonomy. From the patterns of morphological variation among the examined populations of karyotypically characterized individuals, we offer hypotheses that should be tested in the development of formal intraspecific taxonomic decisions.