Background:Lamivudine is an inhibitor of HBV replication which is efficient and well tolerated in adults with chronic hepatitis B.Data regarding the effect of extended Lamivudine treatment in children who failed to respond to previous IFN a therapy are scarce.Therefore,the effects of Lamivudine treatment on ALT activity,HBV DNA,HBeAg and HBsAg seroconversion as well as the occurence of YMDD variant and adverse effects were determined.Material/Methods:The observation was carried out on 41 children,aged 4 –17 years,with biopsy-proven chronic hepatitis B (HBeAg+,HBV DNA+,wild-type virus+),who were nonresponders to previous IFN a therapy.Lamivudine in the dose of 3 –4 mg/kg/day up to 100mg/day was given for 18 months.Results:40 children completed 12 months and 25 of them –18 months of therapy;one boy was excluded from this study due to severe thrombocytopenia.After 6 months of Lamivudine therapy 62.2%of children cleared HBV DNA,59.3% normalized AlAT activity and only 1 child (2.5%)lost HBeAg. After a year of therapy 25%of children cleared HBV DNA, 81.5% normalized ALT activity and 10%lost HBeAg.At the end of 18 months therapy in the group of 25 children 40%of them cleared HBV DNA,20%seroconverted to antiHBe and 76.5%normalized ALT activity.No adverse effects were noted, except thrombocytopenia.YMDD variant was present in 20% of children after one year of therapy and in 32%–6 months later. Conclusions:The 18-month-treatment with Lamivudine in children with chronic hepatitis B who did not respond to IFN a normalized ALT activity in most children and caused seroconversion to antiHBe in 20%.However it was associated with a high risk for developing YMDD mutation.