This study aimed to collect information on the diversity of corals and calcified hydroids of the Manuel Luiz Marine State Park (state of Maranhão, Northeast Brazil) to aid in the development of a management plan for the park. A total of 21 cnidarian species were identified, of which 16 were corals and calcified hydroids. The bathymetric and geographic distribution of each of these species was extended. This area has a rich coral fauna in relation to other parts of Brazil and is comparable in diversity to the Abrolhos Islands (Bahia State) -an unexpected result considering the region's proximity to the Amazon River Basin. Most of the specimens of corals and calcified hydroids observed were bleached.Keywords FD et al. -Biota Neotropica, v7 (n3) -bn00907032007