The opposite homozygotes method was used to assess the individual-grandparent relationships of 2359 pigs in six breeds in the Czech Republic. The % of Mendelian inconsistencies (%conflicts) between SNP genotyped pigs were computed. The relationships of these pigs were divided into groups: parents (P), great-grandparents (GGP), grandparents (GP), half-sibs (HS), parent siblings (PS) and others (O). The second-degree relationship groups (GP, HS, PS) did not differ for %conflicts with each other but differed in P, GGP and O (P < 0.001). The SNP panel of 434 SNPs did not provide the same results (correlation of %conflicts was 56.7 %) as all available SNPs (32318). The GP relationships with known genotypes for individual-parent-grandparent were assumed as verified. The threshold for relationship exclusion was set up to the maximal value of %conflict (16.33) in the GP-verified group. The 26 individual-grandparent relationships would be excluded if the given threshold was applied. The number of unevaluated loci influenced the %conflicts, which should be considered before individual-grandparent relationship exclusion. The method can be valuable for the identification of the wrong individual-grandparent pedigree records.