Three samples of surnames reported in the telephone directory of Cosenza province, Italy, are used, singly and together, to detect the presence of genetic barriers and to analyze the genetic relationship between the Italian and the Italo-Albanian communities living in this area. The genetic structure of the population seems characterized by the distinction between the northern and southern regions of the province. The Sibari plain, endemic with malaria until recently, probably constituted a genetic barrier. In the southern region of the province, the valley along the Crati river (also occupied by malarial fenlands), constituted a genetic barrier between the northern Sila upland and the western coast. Surname similarities between Italians and Italo-Albanians could be the result of gene flow and/or an initial choice of similar surnames; the second possibility accords with the persistence of the Albanian cultural identity and the level of endogamy in Albanian communities. In fact, the coefficient of relationship by isonomy (Ri), which is significantly higher in Italo-Albanians than in Italians, may be the result of genetic isolation and endogamy.