There is a continued need for safe and effective treatments for children and adolescents with chronic hepatitis B. Adefovir dipivoxil (ADV) is a licensed treatment for chronic hepatitis B in adults. This study was designed to characterize the pharmacokinetic profile of adefovir following the administration of 0.14 mg/kg and 0.3 mg/kg of ADV (oral solution) in children aged 2 to 11 years and of ADV 10 mg in adolescents aged 12 to 17 years. Forty-five subjects were included in the pharmacokinetic and safety evaluations. Adefovir was rapidly absorbed. Adefovir levels rose rapidly in the first hour and then declined in a biphasic manner. Dose-proportional pharmacokinetics was observed in the 0.14-mg/kg and 0.3-mg/kg groups. The 0.3-mg/kg dose in children aged 2 to 6 and the 10-mg dose in adolescents resulted in exposures that were comparable to those seen previously in adults given ADV 10 mg. Adefovir dipivoxil was well tolerated at the doses evaluated in this study. Adverse events were generally mild and reported as being unrelated to study medication. There was 1 serious adverse event reported that was not related to study medication. No patient discontinued the study prematurely due to an adverse event related to the study drug.