This study presents the gross and histopathological findings of adenoviral hemorrhagic disease (AHD) in two yearling and one adult mule deer (Odocoileus hemionus). These cases represent the first known outbreak of deer adenovirus (Odocoileus adenovirus 1) in Arizona. Over the span of a month, three female captive mule deer were submitted to Midwestern University's Animal Health Institute for postmortem examination. All of these deer were from the same deer farm and historical findings were similar, consisting of acute presentation of hemorrhagic diarrhea and sudden death. Grossly and histopathologically, all cases had severe pulmonary edema and hemorrhagic enteritis. Additionally, two of the three cases had low numbers of large amphophilic intranuclear inclusions expanding endothelial cells within the small intestine and lungs. Viral PCR of pooled small intestine, lung, and spleen from each of the three cases were positive for deer adenovirus and negative for blue tongue and epizootic hemorrhagic disease.