We evaluated geographic variation in New World porcupines of Coendou (Erethizontidae) from eastern Brazil by analyzing morphological data from museum specimens we identified as Coendou insidiosus and C. spinosus. Coendou insidiosus ranges from the states of Bahia to Espírito Santo, reaching the state of Minas Gerais in Brazil; C. spinosus extends from the states of Minas Gerais and Espírito Santo to the state of Rio Grande do Sul, in Brazil, extending into Paraguay, Uruguay, and northeastern Argentina. Our results indicate that there are three spatially coherent, morphologically distinct groups, which can be diagnosed using a combination of discrete morphological characters, and which are supported by univariate and multivariate statistical analyses. We classified members of the Northern group as C. insidiosus, which usually have several pale to light-brown unicolor thin hairs covering the dorsal and lateral quills. They are cranially and externally smaller than the other two groups, and have shorter hairs and quills. Specimens of the Central group are intermediate in terms of body size, and fit the description of C. spinosus, which have thick hairs covering the dorsal and lateral quills. These hairs are dark-brown at the base, and grayish, orange, yellow or light brown at the tip. The Southern group has the largest size and we classified it as a geographic variant of C. spinosus based on the conspicuous presence of large quills on the dorsal surface, which vary from yellowish or orange to blackish.