The prevalence and the clinical course of hepatitis C virus (HCV) infections were studied in 23 HIV-1-infected children, who were born to 22 mothers with HIV-1/HCV coinfection. During the follow-up only two children (8.7%) showed persistent anti-HCV antibodies and circulating HCV RNA. Both children, who were aged 10 and 10.6 years respectively at the end of follow-up, had chronically-evolving liver disease and autoimmune thrombocytopenia but no signs of progressive HIV disease. Based on our experience, vertically-acquired HIV-1/HCV coinfection is less frequent than is generally reported and may be associated with the development of chronic thrombocytopenia in addition to liver disease. Moreover, perinatal HIV-1/HCV coinfection appears to be associated with a slow progression of HIV disease.