In order to achieve a monophyletic classification of oryzomyine rodents, 10 new genera are described for species or species groups previously referred to the polyphyletic genus Oryzomys. The following names are proposed: Aegialomys, n.gen. (for the “xanthaeolus group” of authors); Cerradomys, n.gen. (for the “subflavus group”); Eremoryzomys, n.gen. (for polius); Euryoryzomys, n.gen. (for the “nitidus group”); Hylaeamys, n.gen. (for the “megacephalus group”); Mindomys, n.gen. (for hammondi); Nephelomys, n.gen. (for the “albigularis group”); Oreoryzomys, n.gen. (for balneator); Sooretamys, n.gen. (for angouya); and Transandinomys, n.gen. (for bolivaris and talamancae). All of the new genera thus constituted are morphologically diagnosable and have distinct ecogeographic distributions. Pending revisionary work that is currently in progress by other researchers, six species belonging to the “alfaroi group” (herein construed as including alfaroi, chapmani, melanotis, rhabdops, rostratus, and saturatior) are provisionally referred to Handleyomys. As a result of these changes, the genus Oryzomys is restricted to the “palustris group” of authors, and the tribe Oryzomyini now comprises 28 genera.