This study reports the phylogenetic relationships of 13 species of lasiurine bats using 4 loci from mitochondrial and Y-chromosomal DNA. Our results support a sister taxon relationship between the red and hoary bats, with the yellow bats being more distantly related. Several taxonomic revisions are suggested based on the results of this study. We support the recognition of 3 separate genera: Lasiurus (red bats), Dasypterus (yellow bats), and Aeorestes (hoary bats, including A. egregius which groups more closely to the hoary bats than its traditional placement with the red bats). We recognize L. frantzii as a distinct species and recognize L. blossevillii salinae as a subspecies rather than species. We elevate 3 previously recognized subspecies of A. cinereus to specific status. The phylogeography of the endangered Hawaiian hoary bat is studied in detail, and hoary bats are found to have undergone multiple invasions of the Hawaiian Islands from North America over its evolutionary history. We also report the presence of 2 species of Aeorestes on the Hawaiian Islands where only one previously had been known.