Résumé
A new species of Hipposideros is described from Vietnam. Morphologically, it is similar to taxa in the Hipposideros armiger complex but is substantially smaller. The new species, which has been found living sympatrically with H. at-linger in Cat Ba National Park, is distinguished from it by size, acoustic characters, and differences in the mitochondria] DNA. Currently, the new taxon is known from Cat Ba Island in Ha Long Bay in northern Vietnam and from Chu Mom Ray National Park, which is situated on the mainland some 1,000 km to the south. It was collected in disturbed and primary forests.