<p>The Block Island meadow vole (<i>Microtus pennsylvanicus provectus</i>) is endemic to Block Island, Rhode Island in the United States of America, and is one of six meadow vole insular subspecies in North America. The Block Island meadow vole has been designated as a subspecies based on morphological examination; however, genetic analyses have not been conducted to test this classification. We tested the subspecies classification by examining mitochondrial DNA sequences from the <i>cytochrome B</i> (<i>cytb</i>) gene of 20 Block Island individuals and 37 mainland individuals from Rhode Island. We identified one nucleotide that was unique to all Block Island meadow voles compared to mainland Rhode Island meadow voles, but the nucleotide was found in a meadow vole sequence from GenBank. Sequencing results revealed three Block Island and eight mainland meadow vole <i>cytb</i> haplotypes. Two haplotypes were detected on Block Island with one haplotype unique to each year and another haplotype shared between years. We suggest that the Block Island meadow vole should continue to be classified as a conservation unit and managed separately from mainland populations. Additional genetic analyses also should be conducted to determine their divergence time from mainland meadow voles, which could elucidate when they colonized Block Island. The Block Island meadow vole is the only endemic taxon on the island, which could have been a natural occurrence or an historic human facilitated introduction.</p>