Haemorrhagic fever with renal syndrome (HFRS) is characterized by fever, headache, abdominal pain, renal dysfunction and various haemorrhagic manifestations. The viruses causing HFRS all belong to the Hantavirus genus in the Bunyaviridae family. At least three of the different hantaviruses are associated with human disease: Hantaan, Seoul, and Puumala viruses. HFRS is endemic in a belt from Norway in the west, through Sweden, Finland, the Soviet Union, China, Korea to Japan in the east. The clinical severity of HFRS varies throughout this belt. A severe form with haemorrhagic manifestations and significant lethality (Korean haemorrhagic fever--caused by Hantaan and Seoul virus) occurs in Asia, while a milder form (nephropathia epidemica caused by Puumala virus) with less haemorrhagic manifestations and no or low lethality is found in Europe. All hantaviruses are spread by rodents where the major route of transmission to man is via aerosol from rodent urine, saliva and faeces. Although HFRS occurs with the same clinical picture in children as in adults both incidence rates and antibody prevalence rates are very low in children under 10 years. Men of working age make up the bulk of clinical cases.