Cavity-nesting birds may frequently compete for a limited supply of nest and roost cavities in trees, but interspecific sharing of these cavities has rarely been reported. The globally vulnerable Helmeted Woodpecker (Dryocopus galeatus), a little-known Atlantic Forest endemic, is believed to be threatened by nest-site competition; however, little is known about its ecology or natural history. I report an observation of a female Helmeted Woodpecker roosting with two White-eyed Parakeets (Aratinga leucophthalma) in their non-excavated (natural) nest cavity at Cruce Caballero Provincial Park, Argentina, and discuss possible implications for ecology and conservation of this rare woodpecker.