Data in this study confirm the validity of a species of muntjac, Muntiacus rooseveltorum, that has been controversial for 60 years. Diagnostic DNA characters are presented for each species examined including the M. rooseveltorum holotype. Three specimens of a recently collected small Laos barking deer have identical sequences to the type specimen of M. rooseveltorum. These DNA characters unambiguously diagnose the newly collected specimens as M. rooseveltorum. This study highlights the importance of continued field surveys in remote regions and the utility of diagnostic DNA characters in identifying species.