The discovery of the leaf deer Muntiacus putaoensis in northern Myanmar has added to the growing list of large mammals recently discovered in remote, unex- plored parts of south and south-east Asia. Its subsequent discovery in eastern Arunachal Pradesh, India, based on morphometric analyses of two skulls collected from local hunters, doubled the size of its known east-west range, which is significant for a newly-discovered and poorly understood species. However, ambiguity remained regarding several other partial skulls and dried skin samples collected during subsequent surveys. The sympatric occurrence of the Indian muntjac Muntiacus muntjak further complicates species identification based primarily on morphometry. In this paper, we develop molecular genetic analyses that can unambiguously identify muntjac species. Further, we test and apply our methods to unknown skin samples to confirm the occurrence of the leaf deer in Arunachal Pradesh. Finally, we use our samples and genetic data from three mitochondrial markers to establish phylogenetic affinities between these samples and other extant members of the Muntiacus genus. Our approach, which combines the use of specific primers and phylogenetic analyses, is generally applicable towards the detection of cryptic biodiversity in unexplored and species-rich areas like north-east India.