Hyloxalus edwardsi and H. ruizi are high-Andean dendrobatid frogs that inhabit the Cordillera Oriental of Colombia. Both species were placed in the H. edwardsi group on the basis of the synapomorphic presence of an elongate cloacal sheath and the absence of a tarsal keel and vocal slits. The group was originally placed in Colostethus sensu lato and was subsequently transferred to Hyloxalus; however, no species of the group were included in previous phylogenetic analyses. Both species are critically endangered, and recent expeditions to their type localities have yielded no additional specimens. Nevertheless, on the western flank of the Cordillera Oriental of Colombia, we discovered a population possessing the elongate cloacal sheath but with other morphological character states that differentiate it from the previously known species. On the basis of this new material and examination of H. edwardsi, H. ruizi, and other Andean dendrobatids, we describe this population as a new species and test the phylogenetic position of this group. Our results corroborate the placement of this group within Hyloxalus, specifically as sister to H. picachos, thereby refuting the monophyly of the recently proposed H. subpunctatus clade. We also identify several new putative morphological synapomorphies of the H. edwardsi group related to the extrinsic cloacal musculature and the subarticular tubercles of the hand. Although the cloacal sheath character is still taxonomically useful, given the inherent difficulty in scoring it unambiguously on the basis of external morphology, we deprecate it for phylogenetic analysis in favor of the internal morphological characters.