The Hawaiian Archipelago is one of the most isolated island chains on Earth, and is known for a high proportion of endemism in its coral-reef fish fauna (Randall 2007). In the Northwestern Hawaiian Islands (NWHI), percent endemism based on numerical densities increases with latitude on shallow coral reefs (<30 m), and peaks at 62 % at Pearl and Hermes Atoll (Friedlander et al. 2009). On mesophotic reefs (50–80 m) of the NWHI, endemism was also found to increase with latitude, reaching a peak of 92 % at Midway Atoll (Kane et al. 2014). Here, we report the highest levels of endemism recorded from the deepest coral reefs at the northernmost atoll in the world.