Cosmoledo Atoll, in the Aldabra Group, western Indian Ocean, has rarely been visited by scientists. This paper reports the first visit by ornithologists during the south-east monsoon when many seabirds breed. The breeding populations of three species of booby (Sula spp.) and of Sooty Tern Sterna fuscata were censused and all other species of bird seen were recorded. The atoll proved to have globally significant populations of Masked Booby Sula dactylatra of the subspecies melanops, Red-footed Booby S. sula of the subspecies rubripes, and Sooty Tern of the subspecies nubilosa. Cosmoledo also supports populations of landbirds that have forms endemic to the Aldabra group, but whose taxonomy requires examination using molecular techniques. The atoll, although currently uninhabited, suffers the impacts of exotic fauna and flora, including cats and rats, introduced by previous inhabitants. The isolation of Cosmoledo confers some protection, but its value as a centre of biodiversity, and designation as an Important Bird Area by BirdLife International, indicate that formal protection is needed. Political mechanisms for this are suggested, the implementation of which would help to procure funding to enable practical conservation of the atoll's biota.