Aim: To investigate the potential of false inclusion of a close genetic relative in paternity testing by using computer generated families. Methods: 10 000 computer-simulated families over three generations were generated based on genotypes using 15 short tandem repeat loci. These data were used in assessing the probability of inclusion or exclusion of paternity when the father is actually a sibling, grandparent, uncle, half sibling, cousin, or a random male. Further, we considered a duo case where the mother's DNA type was not available and a trio case including the mother's profile. Results: The data showed that the duo scenario had the highest and lowest false inclusion rates when considering a sibling (19.03 ± 0.77%) and a cousin (0.51 ± 0.14%) as the father, respectively; and the rate when considering a random male was much lower (0.04 ± 0.04%). The situation altered slightly with a trio case where the highest rate (0.56 ± 0.15%) occurred when a paternal uncle was considered as the father, and the lowest rate (0.03 ± 0.03%) occurred when a cousin was considered as the father. We also report on the distribution of the numbers for non-conformity (non-matching loci) where the father is a close genetic relative. Conclusions: The results highlight the risk of false inclusion in parentage testing. These data provide a valuable reference when incorporating either a mutation in the father's DNA type or if a close relative is included as being the father; particularly when there are varying numbers of non-matching loci.