The present work has two aims: to give an updated revision of the genus in Argentina. including a key, and to propose specific characters not included in previous revisions. Perithemis waltheri Ris is considered as a junior synonym of P. icteroptera (Selys). The first description of the last larval instar of P. icteroptera, and a redescription of the last larval instar of P. mooma from Argentina are included.