Reactivation of HBV is a well known complication in patients undergoing HSCT. Lamivudine treatment appears to prevent hepatitis B virus reactivation and to decrease the mortality in at risk HSCT patients. We describe HBV reactivation occurred in three allogeneic HSCT pediatric patients coming from Eastern Europe, one of whom was successfully treated with lamivudine. Our experience confirms that HBV-DNA may persist as intra-hepatic infection or in extra-hepatic sites and that HBV reactivation may appear during immunodepression. Careful and complete screening for HBV markers is mandatory before HSCT, especially in children coming from countries at risk for HBV. Furthermore, a treatment with lamivudine could also represent an efficacious prophylaxis in pediatric patients to avoid HBV reactivation and to decrease the development of severe hepatic disease.