During an outbreak of haemorrhagic fever with renal syndrome (HFRS) in 1989, five children (3 girls, 2 boys, aged 6.8-16 years) with a severe form of the disease were treated; four of these were followed for 22-28 months. The main clinical features in all five patients were: fever, headache, myalgia, abdominal and back pain and vomiting; haemorrhagic syndrome was present in four children. Renal syndrome presented with severe acute renal failure in all five patients. All patients recovered. Serological confirmation by an indirect immunofluorescence assay, by enzyme immunoassay for IgM antibodies and by plaque reduction neutralization test showed infection by Belgrade virus in three and by Hantaan virus in two patients. It was not possible to differentiate these two serogroups on the basis of clinical features. This study provides further information on the circulation of different hantaviruses causing severe HFRS in Serbia.