Results from a phylogenetic study of the evolution of the parasitic bat flies, Streblidae and Nycteribiidae are described. The relationships within and among these families have been investigated using molecular data from the 18S rDNA nuclear gene, and the 16S, cytochrome oxidase II, and cytochrome B mitochondrial genes, for a total of 3048 molecular characters. Phylogenetic trees were reconstructed using maximum parsimony, maximum likelihood, and Bayesian methods. Some previous hypotheses indicate that streblids and nycteribiids are sister families, with the nycteribiids, which exhibit more extreme morphological changes associated with the parasitic lifestyle (i.e. loss of wings, dorsally shifted head and leg insertion), as the older lineage of the two. However, the results of these analyses indicate that a monophyletic Nycteribiidae is nested within the streblid clade, rendering Streblidae paraphyletic. We present evidence for two independent invasions of this group into the new world, once within the nycteribiid lineage and once in the paraphyletic streblid lineage (subfamilies Nyctyerophiliinae, Streblinae, Trichobiinae).