This study examines the Sciuravidae, an important but little-studied family of primitive Eocene rodents that has been postulated as ancestral to the Muroidea, Dipodoidea, Castoroidea, Geomyoidea, and Caviomorpha. A cladistic analysis will be presented on relationships of all postulated sciuravid genera and primitive members of potential sister taxa, using Paramys and Cocomys as outgroups. The analysis is based on dental and, where available, skull and postcranial material from fossils, casts, and published descriptions. Results test taxon monophyly and clarify the relationships of early rodent groups. Potential biogeographic and biostratigraphic implications, such as the existence of stable faunal provinces or biogeographic refugia, are examined. The results of this study will be compared with molecular phylogenetic studies to clarify problematical evolutionary divergences. The origins of this most speciose and diverse group of mammals are surprisingly uncertain given the breadth and time depth of the information available on the group; a robust phylogeny cannot help but clarify the early history of the rodents.