The endemic Australian eusirid amphipod genus Sancho Stebbing, 1897, is revised based on new material. A neotype is established for Sancho platynotus Stebbing, 1897, which is redescribed, and the new species S. kuiteri is described. Members of Sancho are considered to be obligate commensals of sponges. Their depressed body form and entire telson may be an adaptation to their commensal life-style, but their cantilevered second gnathopods may indicate a phylogenetic relationship with the Eusirus-like members of the Eusiridae.