Abstract
Genetic exclusion of siblinghood of two persons, without parental findings, is basically not possible. Both the positive and the negative proof of descent can only be provided by statistics. Our aim is to evaluate the likelihood ratio (LR) and posterior probability (W-value) sufficient for a secured statement. Further, we evaluate the influence of the number of analysed STR systems on the LR-value by analysing different numbers of loci for 1225 unrelated couples and 61 pairs of full-sibs and testing the hypotheses full sibs versus half sibs versus unrelated.