Populations of harlequin frogs Atelopus are declining throughout their geographical range. In Peru six of the 11 nominally described species are Critically Endangered, and there are at least 17 undescribed additional forms (all representing apparently distinct species), the conservation status of which is unknown. Most Atelopus taxa in Peru have relatively small geographical ranges, some known only from single populations, and have only a limited chance of survival. Conservation will require: (1) improvement of the faunistic and taxonomic knowledge of the genus, (2) field surveys, including in remote areas, (3) assessment of all species and populations for chytridiomycosis and research on the agent's biology, (4) ex situ conservation measures to facilitate later reintroduction, and (5) involvement of national and international conservationists and local people. © 2005 FFI.