The Staphyliniformia is one of the most diverse lineages of Coleoptera, with representatives occupying every conceivable non-marine niche. Phylogenetic relationships among its varied families and lower taxa have defied resolution. The problem has been further complicated by the recent suggestion that another major coleopteran series, Scarabaeiformia, is derived from within it. Here we present the first phylogenetic analyses, based on 18S rDNA sequences and morphological data, to explicitly examine this possibility. Thorough evaluation of alternative alignments and tree construction methods support the contention that Scarabaeiformia is derived from within Staphyliniformia. Though the analyses yielded strong support for few family level groupings within the expanded Staphyliniformia, they conclusively support a close relationship between Hydraenidae and Ptiliidae, which has often been debated. The primary factor hindering additional resolution appears to be the inconsistent rate of divergence in 18S among these taxa.