We visited San Ambrosio Island off northern Chile (26 degrees 21'S, 079 degrees 47'W) on 10-12 December 2019. We found a large population of Kermadec Petrel Pterodroma neglecta juana that appeared to be healthy. In the area that we could survey, we estimated at least 22686 breeding pairs, which is an underestimate of the entire population as we could not access some steep areas. Introduced mammals, which have since been eradicated, caused a loss of island vegetation that might be a drawback for this population, as shading from the sun appears to be important for nest-site selection. Egg-laying started by early December. We assessed 223 birds with respect to coloration: most birds were intermediate phase (65%) and the rest were either very dark (23%) or very pale (12%). We found skeletal remains of goats and rabbits on the island but no living mammals, although a single goat may still be alive. In the context of an estimated world population of similar to 100000 pairs of Kermadec Petrel, the San Ambrosio Island population contributes significantly.