This dataset comes from a project that was undertaken to assess the reef health, status, fisheries potential, conservation value and biodiversity on Rongelap Atoll. There is much interest from the local Government for the management of marine resources and the plans to re-inhabit the islands are imminent. The work carried out on the expedition in Rongelap was for the Rongelap Atoll Local Government (RALGov) to assess their marine resources, on which to base new eco-tourism and sport diving and fishing ventures. The project team surveyed 12 sites around Rongelap Island from shore and a further 2 sites on other islands west of Rongelap Island. The results show that this area could be divided into 5 biogeographical zones, encompassing lagoon sites, outer reef sites and passes. The outer reef zone showed the highest coral cover and species richness. A high proportion of food fishes was also found in these zones, although a different suite of fish species was abundant and large inside the lagoon. High fish biomass, high percentages of coral cover and a total species number of 361 fishes and 170 corals indicated that the reefs around Rongelap Island are outstandingly pristine and healthy. Considering the small size of the area surveyed, it is exemplary that the reef supported more than two thirds of all fishes known from the Marshall Islands.