It is known that autosomal unlinked markers are unable to distinguish some pedigrees (such as grandparent/grandchild, avuncular and half-siblings). This poses a problem especially in cases of identification in mass disasters, other human remains, or in heritage cases where it is crucial to define kinships. Theoretically, X-short tandem repeats (X-STRs) analysis should allow distinction of some of those pedigrees and so a practical approach was undertaken in order to quantify the informative power of a set of X-STRs currently available in the forensic community. Therefore, female/female, female/male and male/male individual pairs, linked by the above-mentioned kinships, were tested using Investigator Argus X-12 kit. For different combinations of 2 alternative hypotheses, Likelihood Ratios (LRs) were calculated for 89 female/female, 68 female/male and 63 male/male combinations of (autosomally) indistinguishable pedigrees. When LRs are assessed considering exactly one pedigree in which incompatibilities are possible, satisfactory values are obtained favouring one of the relationships. Apart from these cases, LRs were, in average, low and, in many cases, against the pedigree known to be under analysis.