The importance of X-chromosome markers in individual identifications, population genetics, forensics and kinship testing is getting wide recognition. In this work, the authors studied the distributions of 25 X-chromosome single nucleotide polymorphisms (X-SNPs) in population samples from Northern, Central and Southern Portugal (n=305). The data were also compared with previous data from the Mediterranean area confirming a general genetic homogeneity among populations in the region. The X-SNP distribution in the three Portuguese regional samples did not show any significant substructure and the X-SNP distributions did not differ significantly from those of the majority of Mediterranean populations. (Published Abstract)