Phylogenetic relationships among swifts of the morphologically conservative genus Chaetura were studied using mitochondrial and nuclear DNA sequences. Taxon sampling included all species and 21 of 30 taxa (species and subspecies) within Chaetura. Our results indicate that Chaetura is monophyletic and support the division of the genus into the two subgenera previously identified using plumage characters. However, our genetic data, when considered in combination with phenotypic data, appear to be at odds with the current classification of some species of Chaetura. We recommend that C. viridipennis, currently generally treated as specifically distinct from C. chapmani, be returned to its former status as C. chapmani viridipennis, and that C. andrei, now generally regarded as synonymous with C. vauxi aphanes, again be recognized as a valid species. Widespread Neotropical species C. spinicaudus is paraphyletic with respect to more range-restricted species C. fumosa, C. egregia, and C. martinica. Geographically structured genetic variation within some other species of Chaetura, especially notable in C. cinereiventris, suggests that future study may lead to recognition of additional species in this genus. Biogeographic analysis indicated that Chaetura originated in South America and identified several dispersal events to Middle and North America following the formation of the Isthmus of Panama.
