Using a realistic model of meiotic crossing over the variability in full sib genetic identity is estimated by simulating 200 independent pairs of sibs. The standard deviation of the percentage of the autosomal genome identical by descent (IBD) was found to be about 0.056. Simulations of sibships larger than size two revealed that the average within sibship standard deviation is between 0.054 and 0.056, thus indicating that sib pair variability is insensitive to the nonindependence structure present when considering all possible sib pairs contained in a large sibship.