Mesoplodon peruvianus, a new species of beaked whale, is described on the basis of ten specimens which have either stranded or been captured between 11°12′S and 15°19′S latitude along the coasts of the provinces of Lima and Ica, south central Peru. This is the thirteenth living species of Mesoplodon recognized in the world's oceans. The animals that were examined were uniformly gray above, shading to lighter gray below. This whale is the smallest species of Mesoplodon (maximum body length 3.72 m) and is characterized by its teeth, which are small (31 to 65 mm long), ovate in cross section, and positioned 2.5% to 8.4% of the mandibular length from the anterior extremity, and posterior to the mandibular symphysis. Copyright © 1991, Wiley Blackwell. All rights reserved