Wilderness areas have been widely discussed in the terrestrial conservation literature, whereas the concept of marine wilderness has received scant attention. The recent move to protect very large areas of the ocean and thus preserve some of the final marine wilderness areas is a bold policy initiative. However, some important questions have remained unanswered, such as whether marine wilderness areas support a different composition and abundance of species than do the smaller marine no-take areas (NTAs) that are steadily dotting our coastlines. We present a case study from the world's largest wilderness coral reef NTA, the Chagos Archipelago, and demonstrate that fish biomass is six times greater than and composition substantially different from even the oldest NTAs in eight other Indian Ocean countries' waters. Clearly, marine wilderness does promote a unique ecological community, which smaller NTAs fail to attain, and formal legislation is therefore crucial to protect these last marine wilderness areas.