Neotropical porcupines of the Coendou vestitus group consist of four small-bodied species from northwestern South America that are hypothesized to form a clade on the basis of their unique dorsal pelage composition. In addition to soft wool and barbed quills—hair types widely shared by other erethizontids—the dorsal pelage of vestitus-group porcupines includes what may be called bristle-quills: long, thin, unbarbed quills with flexible tips. The group includes Coendou vestitus Thomas, 1899; C. pruinosus Thomas, 1905; and two new species. The latter provide the first documented records of small porcupines from western Amazonia, where only large porcupines (C. prehensilis and C. bicolor) were previously known. Other small porcupines probably remain to be discovered in Amazonia, where hydroelectric dam projects offer unique (if unfortunate) faunal-sampling opportunities.