We used parsimony analysis of endemicity (PAE) to investigate the distribution patterns of South American lowland forest mammals, focusing on centers of endemism and diversity. We utilized distribution data available for species of marsupials, rodents, and primates that occur in South America. Two grids were superimposed on the distribution maps: a larger one encompassing tropical and subtropical South America, and a smaller and more precise grid covering the Atlantic Forest only. Also, the number of species per quadrat was estimated. The results support the idea that the distribution of this fauna is structured in the form of centers of endemism. In addition, there is good congruence between the areas identified here and those proposed by other authors, reinforcing the value of PAE in this kind of analysis. The hierarchical relationships among areas, however, are not clear and sometimes discordant with other biogeographic analyses.