The dipteran superfamily Asiloidea consists of nine families of generally large flies of the lower Brachycera, including the Asilidae, Mydidae, Therevidae and Bombyliidae. This diverse assemblage includes predators, flower feeders and insect and arachnid parasititoids. In recent years, hypotheses of Asiloid monophyly and interfamilial relationships have been repeatedly tested and variously supported by only limited evidence. Morphologically, a larval spiracle is the single synapomorphy uniting the current construction of the Asiloidea. Molecular studies using 28S ribosomal DNA sequences have also shown only weak support for higher-level asiloid clades. The aim of our comprehensive molecular study is to use multiple genes, including the nuclear protein-encoding gene CAD and 28S ribosomal DNA, to test the monophyly of the superfamily and to further resolve the relationships among the Asiloid Diptera. More than 5000 base pairs for over 30 taxa are analyzed using maximum parsimony and Bayesian methods. The placement of several enigmatic taxa, including the Bombyliidae, Hilarimorphidae, and Apystomyia are addressed in the context of current best estimates of relationships among asiloid families.