The major aim of our study was the assessment of the efficacy of lamivudine therapy in children with chronic hepatitis B (CHB). One hundred and six children with CHB, from 5- to 17-years old, were administered lamivudine 3mg/kg/day, up to 100mg/day, for 48 weeks. To assess the efficacy of the therapy several biochemical and virological parameters were monitored before, during, at the end of treatment and 24 weeks after therapy. The applied therapy resulted in a statistically significant decrease of ALT activity and HBV replication within the studied group. Biochemical and virological responses to anti-viral therapy were simultaneously observed in 38 children (36%), compared with 4 children (9%) in the control group. HBsAg was not eliminated in any of them. The response was worse in patients with a high level of HBV viremia before treatment. However, the initial level of ALT activity did not influence the final outcome of the therapy. The effectiveness of lamivudine was also unaffected by other tested factors, such as: route of transmission, duration of infection, undergone IFN therapy. Lamivudine seems to be an effective and well-tolerated antiviral drug in children with CHB. However, further studies are necessary to optimize this therapy.