The Y-specific STR loci DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS434, DYS437, DYS438, DYS439 and GATA A10 were studied in a northern Portuguese population. Haplotype and allele frequencies of these 14 Y-chromosome STRs were estimated. In a sample of 212 individuals it was possible to define 196 different haplotypes of which 182 were found only once, 12 were found in 2 samples and the 2 most frequent haplotypes were shared by only 3 individuals. The observed haplotype diversity value was 0.9992. The usefulness of the inclusion of each of these new markers for forensic purposes is discussed by comparing expected and observed increases in haplotype diversity. When combining the new markers (DYS434, DYS437, DYS438, DYS439 and GATA A10) with the classical set (DYS19, DYS385, DYS389I, DYS389II, DYS390, DYS391, DYS392 and DYS393) a 0.68% increase in haplotype diversity was obtained and the number of different haplotypes rose from 157 to 196. When DYS434 was not considered the haplotype diversity was not affected.