We describe 30 new nesting sites of the Crab Plover Dromas ardeola, the main breeding grounds of which were largely unknown, and for which fewer than 30 colonies had been confirmed since 1970. Our survey included 90 islands, 53% of those existing, in the Dahlak and Howakil archipelagoes, and off the coast of central Eritrea. Colony size varied between 20 and 400 nests. We estimate the numbers of Crab Plovers breeding in central Eritrea at 5000–6000 pairs, i.e. about 50% of the known world breeding population. We describe two cases of probable replacement clutches, a feature unrecorded in this species. Black Rats Rattus rattus seem unable to open Crab Plover eggs, and do not seem to be a threat. Crab Plover colonies are traditionally exploited by local fishermen for collection of eggs, an activity that has increased recently. Our new records solve only partially the problem of the ‘missing’ colonies that are required to account for the world wintering population of 60 000–80 000 birds, and thus other breeding sites remain to be discovered, probably in southern Eritrea, Sudan and Somalia. We estimated that there are 4800–6500 Crab Plovers overwintering within central Eritrea, making it an important wintering ground for the species.