The objective of this research was to identify genomic regions associated with clinical mastitis (MAST) in US Holsteins using producer-reported data. Genome-wide association studies (GWAS) were performed on deregressed PTA using GEMMA v. 0.94. Genotypes included 60,671 SNP for all predictor bulls (n = 35,724) and 35,000 cows sampled from the predictor population of 112,895 females. Autosomal SNP with Wald P-values ≤ 5 × 10⁻⁸ were assigned to the closest annotated gene within 25 kbp using BEDTools v. 2.21.0 and the UMD3.1.1 assembly of the Bos taurus genome, and gene functions were determined by a review of the literature. Genes associated with MAST included CARD14 (80.16 Mbp on BTA17) and RPTOR (52.30 Mbp on BTA19), both of which were previously reported to have significant associations with clinical mastitis in Holsteins. Other genes of interest included: MGAT5 (63.11 Mbp on BTA2), which regulates the biosynthesis of glycoprotein oligosaccharides; CGNL1 (52.83 Mbp on BTA10), which is involved in the formation and maintenance of tight cell-cell junctions and mediates junction assembly and maintenance; EPAS1 (28.57 Mbp on BTA11), a transcription factor associated with blood vessel development and the expression of endothelial growth factor; and ANGPT1 (59.13 Mbp on BTA14), which is associated with vascular development and angiogenesis. These genes are of interest because they may be involved in the development and defense of the mammary gland, and possibly associated with changes in milk composition in response to infections of the udder. However, these results represent only statistical associations, and functional validation is needed to determine if these effects are causal, or simply represent correlations with other processes that may represent true causal mechanisms.