In 80% of children with haemophilia treated in our department, screening tests showed the presence of antibodies against the hepatitis C virus (HCV). HCV RNA was detected in serum in 41% of cases. In 20% of cases there were periodic increases in the level of alanine aminotransferase (ALT) activity, and in these cases liver biopsy was performed after factor concentrate replacement. No haemorrhagic complications or pain complaints were reported either during the biopsy or immediately afterwards. In all cases histopathological examination revealed chronic hepatitis type C - chronic mild hepatitis and chronic minimal hepatitis. Eight boys were treated with interferon (INF) alpha. In two cases this therapy was successful. No HCV RNA was detected in serum and transaminase activity was normal during the year following interferon treatment.