We report the discovery of a new singleton species of Oreobates Jiménez de la Espada, 1872, from the Yungas forest of the Amazonian versant of the Andes in Bolivia, infer its phylogenetic position, revisit the phylogenetic relationships of Oreobates, and discuss the conditions that justify description of the species with a single specimen. The new species, Oreobates yanucu, differs from all other Oreobates in a combination of external conditions: granular dorsal skin with scattered warts, finger I longer than finger II, finger tips of fingers III and IV distinctly enlarged and truncate in outline, tips of toes II to V with ungual flaps, head longer than wide, basal webbing between toes I and II and toes II and III, foot length/snout—vent length = 50%, lack of orange, red, or scarlet flecks and blotches in life. Although similar in appearance to O. amarakaeri Padial et al., 2012, O. choristolemma (Harvey and Sheehy, 2005), O. granulosus (Boulenger, 1902), O. sanctaecrucis (Harvey and Keck, 1995), and O. sanderi (Padial et al., 2005)—all of them species from the Yungas of Bolivia and southern Peru conforming a monophyletic group—the new species is nested within a clade, revealed by molecular phylogeny, in which all species share the condition of enlarged finger discs and is sister to O. berdemenos Pereyra et al., 2014, an allopatric species from the Yungas of Argentina. The new species is only known from a single specimen collected in 1999 at 1500 m above sea level within Carrasco National Park (Provincia Chapare, Departamento Cochabamba, Bolivia). Oreobates now includes 24 described species but seven other new species remain to be named formally and we expect the diversity of this group to increase considerably with the exploration of the Andean foothills of Bolivia and Peru.