Hepatitis C virus (HCV) infection remains a major problem in haemodialysis units despite the risk decrease provided by anti-HCV screening of blood. The exact mode of transmission of HCV in the dialysis units remains unclear. To identify the route of the virus and the mechanisms of transmission an investigation into the outbreak of HCV infection in a haemodialysis unit on a molecular level was held: 12 newly infected patients and 14 already infected were investigated by sequencing the 5' untranslated region of the viral genome. The results showed that 3 strains infected new cases and these strains matched those sequenced in already infected patients. Transmission occurred between patients treated on the same shift and also between different rooms. Console and blood or blood product contamination was excluded. Our study gave molecular evidence of patient-to-patient transmission of HCV in a haemodialysis unit. Our data underline the importance of the strict enforcement of standard precautions to prevent HCV transmission and failure of the isolation of anti-HCV positive patients as preventive measure.