The taxonomic validity of the eryopid temnospondyl Glaukerpeton avinoffi Romer, 1952, from the Upper Pennsylvanian Conemaugh Group of North America is confirmed on the basis of a detailed restudy of two specimens: the holotype, based on a partial skull roof from Pittsburgh, Pennsylvania; and the skull and postcranial material of a second specimen from an approximately equivalent stratigraphie level in West Virginia that was originally referred to Eryops cf. E. avinoffi (Romer), but is reassessed here as G. avinoffi. This contradicts a previous redescription of the holotype of G. avinoffi as referable to Eryops Cope, 1882. A single unique feature, the presence of three large, fang-like tusks on the ectopterygoid, distinguishes Glaukerpeton from all other eryopids. A cladistic analysis was performed using 19 cranial and two postcranial characters to clarify the phylogenetic relationships between Glaukerpeton Romer, 1952, and the only other eryopids in which the skull anatomies are well known: the Late Pennsylvanian—Early Permian Eryops and the Early Permian Onchiodon Geinitz, 1861. The resultant cladogram indicates that Eryops and Onchiodon share a more recent common ancestor than either does with Glaukerpeton. The position of Glaukerpeton as a basalmost taxon may indicate that the ancestry of Eryopidae predates the Late Pennsylvanian. The possession of lateral line sulci, ossified ceratobranchials, and a thinly ossified skull roof indicates a probable aquatic habitus of the adult Glaukerpeton. Reconstructions are presented for the first time of the holotypic skull roof in dorsal view and the cranium and mandible of the referred specimen in various views.