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Bahía Blanca is an urban city in a historically and geographically strategic location for the mixture of different populations in Argentina. In the present study, 10 Alu elements from the X chromosome are analyzed to characterize the genetic composition of the city’s population, to compare it with other worldwide populations, and to explore the usefulness of X-chromosome markers for human population genetics purposes. In the Bahía Blanca sample, 7 of 10 Alu insertion frequencies are polymorphic. X-chromosome Alu results in Bahía Blanca are compared with eight different populations from Africa, Europe, and America. Genetic distance analysis indicates that the Bahía Blanca sample is closer to the European and North African samples (average distances of 0.106 and 0.113) than to the Native American (0.163) and sub-Saharan African samples (0.247). Genetic relationships shown by multidimensional scaling illustrate the intermediate position of Bahía Blanca compared with groups in other regions (European, Native American, and African). Admixture results of the Bahía Blanca sample for X-chromosome markers indicate similar proportions of Native American (0.472) and European parental contributions (0.479) and a minor sub-Saharan African contribution (0.049). These results are consistent with the past decade’s genetic studies of Argentinean populations that reported higher Native American and sub-Saharan African contributions than previous data.