A combined paternity index (PIcom) of 13,811.215 and a paternity probability (W) of 99.9999928 percent for alleged father 1 and a PIcom of 35,332.241 with a W of 99.9999971 percent for alleged father 2 was obtained. Inclusion was observed in both fathers. The mestizo database was used. Twelve STRs of the Y chromosome of the commercial kit PowerPlex-Y were analyzed, and alleged father 1 was excluded for presenting a different haplotype. The two tested men were not related, and they did not share a common Y chromosome; however, the authors calculated a likelihood ratio for half-siblings. They share an allele in 16 out of the 19 autonomic STRs, which could indicate they are half-brothers. This information was confirmed with a personal interview to each alleged father and a search on familial pedigree. It is clear that the solution to complex paternities with genetic deficiency requires more genetic information and greater care with the statistical analyses. The authors recommend that the mother also be investigated in all the cases. 3 tables and 19 references