The objective of paper was genomic evaluation for health traits in Holstein cattle. The breeding values and their reliability for clinical mastitis were predicted by single-trait linear animal model with repeatability. The number of cows in dataset was 86,591. The lactation incidence for clinical mastitis was 19.14%. Single-step genomic evaluation method was used to estimate genomic breeding values. The reference population ranged from 37 740 individuals, bulls 54 22, cows and heifers 32 318. The final number of SNPs was 35,295. Number of effective individuals 37,015. Among the genomic animals, 115 animals were suspected to have the same genotype as another individual. These were 107 cows (born 2015 to 2021) and 8 bulls (born 1990 to 2010). These animals were removed from the genomic matrix and the calculation was repeated. The effects on self-estimation were subsequently assessed. We have not been able to prove the impact on genomic breeding values or their reliability. In the reference population used, we identified individuals with a questionable genotype that we propose to remove because they are erroneous. Likewise, we have shown that one of the bulls has been registered twice, under two different names.