At least four individuals of desmostylian are described from a single locality on Unalaska Island, Alaska. Desmostylians are known only from the North Pacific region from Japan to Mexico, but this form is currently unique to Unalaska. It retains certain primitive features, such as relatively low-crowned columnar (desmostylodont) cusps with remnants of cingula, that are shared with Cornwallius. However, it is derived in having additional cusps on lower molars. It also has well-developed upper and lower tusks and a narrow mental symphysis, so far as can be determined. The age of the desmostylian sample is either late Oligocene or (more likely) earliest Miocene. Although the representation of skeletal elements of individuals is low, the presence of a neonate dentary implies that a breeding population of this taxon inhabited, rather than simply dispersed through, the Aleutian Chain during the mid-Cenozoic.