We describe a new species of Telmatobius from cloud forests in the valley of the Río Kosñipata in the Cordillera de Paucartambo, Región de Cusco, Peru, where it inhabits roadside ditches and forest streams. The new species is among the larger Telmatobius known. It has a short rostrum and exceedingly long jaw. Males have nuptial excrescences composed of minute, closely spaced spicules. Osteologically, the new species is distinguished by unusual ossification of the endocranium. The sphenethmoid is synostotically united with the prootic and the ossification/mineralization of the dorsal neurocranial roof eliminates the parietal fontanelles, leaving only a small frontal fontanelle. Osteological comparisons are made between the new species and the 24 other species of Telmatobius for which there is information available in the literature. Preliminary evidence suggests that the suspensory apparatus of Telmatobius may have a unique combination of features distinguishing it from that of other anurans. Superficially, the new species resembles members of the Telmatobius bolivianus Group, but its phylogenetic relationships are unknown. Many anurans in the area of the type locality have experienced severe declines, and the new species, not seen since 2007, is considered as Critically Endangered.