After the outbreak of an endemy of HCV infections in the paediatric haematology and oncology wards, epidemiological analysis was performed for cancer children, health-care workers and controls. The study included a total of 639 persons, divided into four groups. The results were as follows: 1) The number of infected paediatric cancer patients was 100/237 (42.4%). 2) Of the 44 health-care workers in the haemato-oncology ward none was infected with HCV. 3) In the other parts of the hospital, five out of 258 (1.9%) permanently employed staff at risk of occupational exposure to blood and other body fluids were infected with HCV; however, the infection rate included only nurses (5/125, i.e. 4%). 4) One hundred adults consecutively tested for anti-HCV antibodies before a planned surgical procedure were not infected with HCV (control group). This study shows that complex nonspecific prophylaxis and full awareness in everyday work has helped to prevent transmission of HCV from highly contagious patients to medical personnel, particularly to nurses who have the highest occupational risk.