The present study analyses three tetranucleotide (DXS7423, DXS8378, DXS6809) and one trinucleotide (DXS7424) X-linked STRs loci in a population sample of North Italy to evaluate their efficiency in forensic applications. The four loci were also used to solve a case of deficiency paternity, in which the question was to establish whether two women were half sisters.