The endemic Seychelles treefrog, Tachycnemis seychellensis (Duméril & Bibron), is restricted to four of the granitic islands of the Seychelles: La Digue, Mahe, Praslin and Silhouette. Megalixalus infrarufus Gunther 1869 is a junior synonym of Eucnemis (Tachycnemis) seychellensis Dumeril Bibron, 1841. Significant variation in colour and morphometric characteristics exists within and between island populations. The patterns of geographic variation revealed support the hypothesis that the distribution of Tachycnemis seychellensis in the granitic Seychelles reflects vicariance through fragmentation of the Seychelles Microcontinent 10,000 years B. P. by marine transgression. However, the possibility of low rates of postfragmentation dispersal between islands cannot be ruled out. The close relationship of the nearby Mahe and Silhouette populations probably reflects prefragmentation gene flow over relatively short distances and postfragmentation stasis due to large population size and similar environments. The small body size and colour similarities of the Praslin and La Digue populations may result from prefragmentation gene flow between these close populations, but the relatively great differences in morphometric traits suggest rapid divergence in isolation perhaps as a result of genetic drift and strong selection. It is argued that the four island populations represent a single species and that subspecies should not be named.