Over the decades, islands have provided a useful background for the evaluation of the consequences of isolation upon populations. Epigenetic and morphometric divergence among black rat (Rattus rattus) populations from Western European island (São Miguel, Terceira, Flores, Porto Santo, Berlenga, Corsica) were analysed and compared with mainland reference populations (Portugal, France, Morocco). Neither of the two approaches showed insular samples to have greater distinctiveness than those from the mainland. The overall pictures of epigenetic and morphometric similarity among populations were concordant, apparently in agreement with their probable origin from founder individuals brought by former maritime traffic. Mainland populations were more variable, but only according to morphometric characters. The adaptive and evolutionary significance of the patterns found may be related to both the period of population isolation and island area.