This paper compares the structures of the surnames of 75 municipal populations living in six north-western Mediterranean regions. Its purpose is to unravel the relations between the local populations in Corsica and Sardinia and the links between these populations and those living in the Italian and French continental territory. On the basis of the matrix of similarity of surnames, some topological representations have been drafted showing the above-mentioned relations between populations under the light of their geographical position, their recent history and studies of genetic analysis. Corsica has an eterogeneous surname structure and evident similarity of the north with Tuscany and some centres of continental France. When only the populations of Sardinia were taken into consideration, it emerged that they differ among each other in relation to their geographical position and their history; when, instead, they were considered in relation to other populations outside the island, it was possible to observe that they form a highly different cluster. This study also identified many differences in the analysed geographical areas of Sardinia. In the minor islands – Elba, Giglio, Capraia – the structure of the surnames has a Tuscan origin as well as some similarity with other geographically distant areas, as in the case of the island of Giglio, if compared with some communities of Liguria.