Technically termed rodent-borne hemorrhagic fevers, these are zoonotic diseases causing several serious syndromes in humans. They are caused by two groups of RNA viruses; of which only one virus in the genus Hantavirus will be discussed. These zoonotic diseases are worldwide in distribution and the particular disease covered herein was first discovered in the southwest U.S. in 1993. Rodents are primarily responsible for the transmission of the virus and they are generally chronically infected, usually asymptomatic, and shed the virus over long periods of time. Because there are few, if any, clinical signs or lesions of infected rodents, most of this chapter emphasizes human safety concerns.