We redescribe Trimeresurus cornutus, a species that has not been reported for more than half a century, based on a recently collected live specimen from the Annamite Mountains of Central Vietnam. Besides new data on the distribution and habitat, we compare coloration and morphological data of the first known male of the species with the type specimen and a third known specimen from North Vietnam. We describe male genital morphology and analyze the systematic relationships of the species using external morphology, hemipenial morphology and molecular data. A phylogenetic hypothesis, based on four mitochondrial genes, suggests that the species is most closely related to Protobothrops jerdonii. The external morphology and hemipenial morphology are consistent with this placement. Based on the few specimens available, Protobothrops cornutus comb. nov. exhibits a very patchy distribution, with an altitudinal range reaching from 150–2000 m.