The colubrid snake Dendrelaphis subocularis is distributed throughout Indochina, the southern limit of its range corresponding with the Isthmus of Kra, an important biogeographic barrier that separates the Indochinese biota from the Sundaic biota. This study presents five museum specimens that represent a hitherto unknown population that inhabits the Sundaic island Java. Thus, the distribution of Dendrelaphis subocularis is disjunct, with the Javan population being isolated by 2000 kilometres from the nearest mainland population. Principal Components Analysis was applied to morphological data taken from the five Javan specimens as well as from 26 museum specimens of Indochinese origin. Regression analysis of the spatial pattern of the resulting scores indicated that: 1) the Javan population exhibits negligible morphological differentiation, and 2) a phenetic cline exists from which the Javan population does not appreciably deviate in spite of its isolated status. These findings suggest a vicariant origin of the Javan population entailing climatic changes and formation of land bridges during Pleistocene glaciations. The Javan and Indochinese populations represent independent sister lineages, and are therefore valid species within the framework of a lineage-based species concept. However, to conform to current taxonomic practice, the Javan population is not named separately due to the fact that it is not diagnosable.