Cyclorrhaphan Diptera are an extremely successful clade of ecologically and phylogenenetically important flies. Despite their significance the relationships among lower cyclorrhaphans ('Aschiza') remain controversial in spite of several morphologically based phylogenetic analyses. We sequenced a 2.7-kb fragment of 28S rDNA for taxa representing all lower cyclorrhaphan families (except Ironomyiidae), four schizophoran families, and seven empidoid out-group taxa. Phylogenetic analysis of these data strongly supports a monophyletic Cyclorrhapha (including the enigmatic taxon Opetia nigra) that is divided into two clades - a well-supported Eumuscomorpha (Syrphidae + Pipunculidae + Schizophora), and a weakly-supported Platypezoidea (all non-Eumuscomorpha). Consequently, the former grouping known as Aschiza, which included syrphids and pipunculids, is not a valid monophyletic clade. Within Platypezoidea, most of our analyses place Lonchopteridae as sister group to Opetiidae, and strongly support the monophyly of Sciadoceridae + Phoridae. Among the Eumuscomorpha we do not recover the monophyly of Syrphoidea (Syrphidae + Pipunculidae). Instead, all analyses place Pipunculidae as the sister group to Schizophora. This novel finding has never been proposed based on morphological data and will require more data (both molecular and morphological) and taxa to confirm.