External and internal head structures and external structures of the thorax and abdomen of larval representatives of Melandryidae (Orchesia), Ulodidae (Meryx), Oedemeridae (Pseudolycus) and Pythidae (Pytho) are described. The obtained data were compared to characters of other tenebrionoid larvae and to larval characters of other representatives of Cucujiformia. Characters potentially relevant for phylogenetic reconstruction are listed and were analysed cladistically. The data set is characterised by a high degree of homoplasy and the resolution of the strict consensus trees of 2650 or 815 (second analysis) minimal length trees is low. The monophyly of Tenebrionoidea is supported by several larval autapomorphies, e.g. posteriorly diverging gula, anteriorly shifted posterior tentorial arms, asymmetric mandibles and the origin of several bundles of M. tentoriopharyngalis from the well-developed gular ridges. Several features of the larval head are plesiomorphic compared to the cleroid-cucujoid lineage. The interrelationships of most tenebrionoid families not belonging to the pythid-salpingid and anthicid-scraptiid groups were not resolved. Synchroidae were placed as sister group of a clade comprising these two lineages and Prostomidae. A sistergroup relationship between Trictenotomidae and Pythidae seems to be well supported and the monophyly of the anthicid-scraptiid lineage was also confirmed. Another potential clade comprises Prostomidae, Mycteridae and Boridae, and possibly Pyrochroidae (s.str.) and Inopeplinae. The monophyly of Salpingidae (incl. Othniinae and Inopelinae) and Pyrochroidae (incl. Pedilinae) was not supported. Many features such as the shape of the head and body, sutures and ridges of the head capsule, the endocarina, the mandibles, the maxillary apex, and also characters of the terminal abdominal apex are highly variable, even within families. Especially the families Tetratomidae, Melandryidae, Colydiidae and Zopheridae show a high degree of variation in the larval stages. Several taxa appear isolated in terms of larval morphology within the families they are assigned to, e.g. Orchesia within Melandryidae, Sphindocis (Sphindocinae) within Ciidae, Calopus (Calopinae) within Oedemeridae and Penthe (Penthinae) within Tetratomidae. A broader spectrum of characters and a stepwise approach will be needed for a reliable clarification of the relationships within a very complex group like Tenebrionoidea.