In the spring of 1993 an outbreak of a new illness caused by a new pathogen was identified in the southwestern United States. This infection struck relatively young, healthy individuals, was characterized by fever, myalgias, respiratory failure, and a high mortality rate. This illness was caused by a new hantavirus and has been termed hantavirus pulmonary syndrome (HPS). The virus is carried by rodents, shed in saliva, urine, and feces. Human infection occurs through inhalation of aerosolized virus. The clinical syndrome has many non-specific signs and symptoms, but does follow a typical course with characteristic laboratory and radiographic findings. Early recognition of this infection is important so maximal supportive care can be initiated. We report the first documented case of hantavirus pulmonary syndrome in Wisconsin and Illinois.