Internal and external features of the head of larvae of Rhysodidae were analyzed phylogenetically. A detailed description of the head of the larva of Omoglymmius hamatus (LeConte) is given. Omoglymmius and Rhysodes belong to a monophyletic unit which is characterized by an isolated submental sclerite and a strongly elongated prementum. The presence of a broad, undivided submental plate is a possible synapomorphy of Rhyzodiastes and Clinidium. The following features are considered autapomorphies of Rhysodidae: head extremely widened posteriorly, stemmata absent, frontoclypeolabral apotome strongly extended posteriorly, snout-like nasal projection, maxillolabial complex retracted, galea extremely modified, caudal premental apotome, labial palpi 1-segmented. Significant features indicate a sister-group relationship between Gyrinidae and the remaining Adephaga. Rhysodidae belong to a monophyletic group which comprises Geadephaga excl. Trachypachini. A sistergroup relationship between Rhysodidae and all other taxa of this monophylum is proposed as a working hypothesis. The wood-boring, xylophagous-fungivorous habits of Rhysodidae are almost certainly a secondary feature as indicated by the absence of the mandibular mola and other features. The hypothesis of a close relationship between Rhysodidae and Scaritini does not accord with the results of this study.