We investigated causes of antler deformities in mule deer (Odocoileus hemionus) bucks from the Paunsaugunt Plateau in southern Utah, US. A total of 10 hunter-harvested and nine live-captured bucks with antler deformities and six hunter-harvested and 43 live-captured bucks with normal antlers were included in the study. All were screened by serology for exposure to epizootic hemorrhagic disease virus (EHDV) types 1, 2, and 6, bluetongue virus, Brucella abortus, Brucella ovis, caprine arthritis, encephalitis virus, and bovine viral diarrhea virus (BVDV) types 1 and 2. Serum testosterone and trace minerals concentrations were measured, and whole-blood counts evaluated. Testicular tissue from the hunter-harvested bucks was tested by quantitative PCR for EHDV-1, -2, and -6. All bucks with antler deformities had low to non-detectable serum testosterone concentrations from end-stage fibrosing orchitis, and EHDV-2 was detected by quantitative PCR in one of the testicular tissues tested. All bucks with antler deformities were seropositive for EHDV-2. In comparison, only 53% of bucks with normal antlers were EHDV-2 seropositive. More than 67% of hunter-harvested and live-captured bucks had antibodies to BVDV-1 and BVDV-2, probably because of high cattle exposure in the area. Our results support previous research linking infection with EHDV-2 to development of antler deformities; however, it remains unclear why some infected bucks develop testicular fibrosis, and others recover from the infection.