Haplotype and allele frequencies of 12 Y-chromosome short tandem repeat (Y-STR) loci (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385 a/b, DYS437, DYS438 and DYS439) included in the Powerplex(R) Y System were determined in seven western Mediterranean populations from Valencia, Majorca, Ibiza (eastern Spain), Sicily and three Calabrian provinces (southern Italy). Amongst the 554 males included in the study, 443 different haplotypes were observed of which 372 were only observed once. The other haplotypes were shared by two to seven men. The overall haplotype diversity was 0.9988 +/- 0.0002. These Y-STRs markers showed a low capacity of discrimination (56.3%) in the Ibiza population probably due to genetic drift. Comparisons between the populations studied and other neighbouring populations showed a clear genetic sub-structure in the western Mediterranean area.