Upper milk molars of oreodonts, hitherto not adequately known, are described for the genera Merycoidodon, Promerycochoerus, Merychyus, Cyclopidius, and Hypsiops. General and sometimes specific differences show up clearly in these teeth. The milk teeth do not support the transfer of Merycoidodon gracilis to Miniochoerus. The patterns of the milk teeth are in accord with the phylogenetic tree given by Thorpe. The milk molars apparently are all replaced at or near the same time, and after all the permanent molars have erupted. There is progressive molarization of the deciduous molars.