The beetle suborder Adephaga consists of several aquatic ('Hydradephaga') and terrestrial ('Geadephaga') families whose relationships remain poorly known. In particular, the position of Cicindelidae (tiger beetles) appears problematic, as recent studies have found them either within the Hydradephaga based on mitogenomes, or together with several unlikely relatives in Geadephaga based on 18S rRNA genes. We newly sequenced nine mitogenomes of representatives of Cicindelidae and three ground beetles (Carabidae), and conducted phylogenetic analyses together with 29 existing mitogenomes of Adephaga. Our results support a basal split of Geadephaga and Hydradephaga, and reveal Cicindelidae, together with Trachypachidae, as sister to all other Geadephaga, supporting their status as Family. We show that alternative arrangements of basal adephagan relationships coincide with increased rates of evolutionary change and with nucleotide compositional bias, but these confounding factors were overcome by the CAT-Poisson model of PhyloBayes. The mitogenome + 18S rRNA combined matrix supports the same topology only after removal of the hypervariable expansion segments. Densely sampled mitogenomes, analyzed with site heterogeneous mixture models, support a plausible hypothesis of basal relationships in the Adephaga.