Chrysomya Robineau-Desvoidy (Diptera: Calliphoridae) is a genus of blowfly commonly observed in tropical and subtropical countries of the Old World. Species in this genus are vectors of bacteria, protozoans and helminths, cause myiasis, are predators of other carrion insects, and are important forensic indicators. Hypotheses concerning the evolution of sex determination, larval anatomy and genome size in Chrysomya have been difficult to evaluate because a robust phylogeny of the genus was lacking. Similarly, the monophyly of subgenera was uncertain. The phylogeny of Chrysomya spp. was reconstructed based on 2386 bp of combined mitochondrial cytochrome oxidase subunit I (COI) and nuclear carbamoylphosphate synthetase (CPS) genes. Maximum parsimony (MP), maximum likelihood (ML) and Bayesian analysis (BA) differed only slightly in the resulting tree topology. Chrysomya was monophyletic. Monogenic reproduction is almost certainly derived rather than, as has been suggested, primitive within the genus, and tuberculate larvae probably evolved twice. Genome size is more likely to have decreased over evolutionary time rather than, as has been suggested, increased within the genus, but its correlation with developmental time was not observed. The subgenera Microcalliphora, Eucompsomyia and Achoetandrus were recovered as monophyletic.