The populations from the Azores islands have been the target of several genetic studies, using data derived from monoparental and recombining genetic systems. These studies have provided a complex picture of the genetic landscape of the three groups of Azorean islands, and further data are required to assess its genetic profile. We present a study of the polymorphism in 10 X-chromosome STR loci (DSXS8378, DXS9898, DXS7133, GATA31E08, GATA172D05, DXS7423, DXS6809, DXS7132, DXS9902, DXS6789) conducted on a total of 304 chromosomes (97 females and 110 males) of unrelated individuals with Azorean ancestry. Average gene diversity was 74.47%, ranging from 66.21% (DXS7133) to 81.19% (GATA172D05). No shared haplotypes were found. Genotype frequencies among females displayed conformity with Hardy-Weinberg expectations for all loci. Pairwise linkage disequilibrium tests did not reveal evidences of association between the studied markers. Significant differences in allelic frequencies between the Western and the Eastern group of islands are in agreement with previous results from mitochondrial DNA and Y chromosome studies, providing further evidence that the Azores cannot be considered an homogeneous population. Moreover, differences between the Western group and the North of Portugal are also reported, supporting the pertinence of a specific database for the Azores populations, on what concerns the genetic markers analyzed. Am. J. Hum. Biol. 22:221223, 2010. Copyright © 2009 Wiley-Liss, Inc.