Ganciclovir therapy was given intravenously to 20 children with cytomegalovirus (CMV)-associated liver disease, of whom 6 were immunocompetent and 14 were immunocompromised (9 had AIDS and 5 had solid tumors). Immunocompetent children had isolated liver disease diagnosed at birth (4 children), or systemic congenital CMV infection including liver disease (2 children). Ganciclovir was used following two regimens: A) 5 mg/kg twice daily for 8 to 86 days (mean 21); B) 7.5 mg/kg twice daily for 14 days followed by 10 mg/kg three times weekly for three months. CMV infection was diagnosed by viral isolation, detection of viral antigens, and/or CMV DNA from blood and urine. All immunocompetent children had negative CMV culture and CMV DNA detection from blood and/or urine after 14 weeks of treatment. However, the three children who were treated with regimen B showed normal ALT levels at the end of the maintenance course, whereas the children who received ganciclovir with regimen A had normal ALT levels only after about 1 year. All children with tumors initiated regimen B, but only three, who had negative CMV detection and markedly decreased ALT levels, received full treatment; of the remaining two children, one recovered after only an initial course, and the other had therapy interrupted because of hepatic failure and died 9 days later. In contrast, the children with AIDS received several ganciclovir courses for different periods at the lower dosage: they generally improved during treatment but did not recover completely, and five children died with active CMV infections. Based on our study, CMV-associated liver disease can be efficiently treated with ganciclovir both in immunocompetent and immunodeficient children. However, a single ganciclovir course including a higher dosage and prolonged therapy appeared to be more effective than several courses with lower dosages.