This paper aims at analysing the distribution of surnames over the Alto Adige-Südtirol, which is an Italian alpine sub-region coinciding with the province of Bolzano-Bozen. Two thirds of the Alto Adige-Südtirol inhabitants are German mother-tongue, whereas the remaining one third is Italian mother-tongue. There is also a minority represented by Ladin-speaking people. Analyses were carried out using a similarity index between different populations, resulting from heads of family surnames distribution over the area. The specificity of the most frequent surnames was also studied. Mapping of surnames took place at municipality level. Municipality populations were grouped according to their valley of residence and territorial geologic and morphological features. The results were interpreted also in the light of historical events and the presence of specific languages or dialects. The geographic neighbourhood, the geo-morphological features of the territory and the easy individual mobility are the main elements for the relations among people living in the valleys of Alto Adige-Südtirol. The ancient ethno-historical substratum is detectable in the spread of the specific languages and dialects, nevertheless it does not play a discriminative role in the above mentioned relations. The socio-economic factors have contributed both to root the autochthonous people in certain places and to modify the structure of surnames in some valleys.