Recently two Flaviviridae-like viruses have been discovered and named GB virus C and hepatitis G virus. Molecular characterization showed them to be different subtypes of the same virus. An association with posttransfusion hepatitis and with sporadic and fulminant hepatitis was reported, but most infected people remain asymptomatic. Data concerning hepatitis G virus infection in infants and children have not been reported to date. The prevalence of hepatitis G virus infection in children after transfusion of blood products in the neonatal period was studied. Serum samples from 251 children, who had received blood products in the first 4 weeks of life and who had been reexamined as part of another study at a mean interval of 37 months (range, 10-70) after last transfusion, were analyzed for hepatitis G virus infection. Follow-up examinations were performed in 14 of 19 hepatitis G virus-positive children 12 to 17 years after the last transfusion. Presence of hepatitis G virus RNA in serum was determined by a reverse transcription polymerase chain reaction assay with nested primers from the helicase region of the hepatitis G virus. To prove specificity of the hepatitis G virus, reverse transcription polymerase chain reaction assay and compare follow-ups with initial sequences, direct sequencing of the NS3 and NS5 regions of the hepatitis G virus was performed. Hepatitis G virus RNA was detected in 19 of 251 patients (7.6%); sequence analysis showed the isolates to be of hepatitis G virus type. None of the patients with hepatitis G virus infection had evidence of liver disease, although 3 patients were coinfected with hepatitis C virus. Four of 14 patients who were reinvestigated after a mean of 15 years showed persistent hepatitis G virus infection. Each of the 4 children was healthy. In none were clinical signs of liver disease observed; liver function test results were within the normal range. Children receiving blood transfusions in the neonatal period are at increased risk of hepatitis G virus infection with a high rate of chronic infection. However, as in the findings in several studies of adult transfusion recipients, in the current results, no association between hepatitis G virus infection and clinical or biochemical signs of hepatitis or extrahepatic disease could be seen.