The family Arenaviridae consists of a unique genus (Arenavirus) that currently comprises 22 viral species, as recognized by the International Committee for Taxonomy of Viruses. Seven newly discovered represent putative new species. Here, our aims were to provide the most comprehensive phylogenetic analysis of members and putative members of the family Arenaviridae to date, and to investigate the genetic diversity observed within and between recognized species of New world arenaviruses to determine whether the genetic criteria previously proposed to define arenavirus species for Old world arenaviruses should be retained or are more widely applicable to the whole genus.