Renal transplantation in patients with chronic hepatitis B virus (HBV) infection is known to be associated with an increased risk for exacerbation of liver dysfunction. Lamivudine has been proven to be a potent inhibitor of hepatitis B virus replication in adults after kidney transplantation. Little is known about its efficacy and safety in pediatric renal transplant recipients. Three cases serve for the discussion to demonstrate the complexity of the clinical course and effective treatment of chronic hepatitis B in pediatric patients awaiting renal transplantation. Two patients on dialysis with a high HBV replication rate were treated with lamivudine before transplantation. After the viral load had decreased below the detection limit, they underwent transplantation successfully. Despite intensified immunosuppression to treat a rejection episode in one and a relapse of the nephrotic syndrome in the other patient, the viral load remained <2.5 pg/mL. Both patients developed a mutation in the YMDD motif of the HBV genome associated with an increase in the HBV replication rate >10,000 pg/mL without deterioration of the liver function. In a third patient with a chronic HBV infection with a low replication rate, lamivudine was started about nine months after kidney transplantation due to an increasing viral load after treatment of an acute rejection episode. Six months later, the HBV DNA was no longer detectable. The patient had no signs of liver dysfunction. Lamivudine in the treatment of chronic HBV infection in pediatric renal recipients seems to be safe and effective in preventing acute liver deterioration. Three clinical cases are discussed with regard to current options in monitoring and antiviral treatment of chronic HBV in pediatric renal transplant recipients.