Hepatitis B virus (HBV) reactivation is the frequent complication after cytotoxic chemotherapy in HBsAg-positive non-Hodgkin's lymphoma (NHL) patients. Pre-chemotherapy viral load may be a risk factor and HBeAg-positive status is associated with increased viral load. The aim of this study was to investigate the long-term treatment outcome of lamivudine in preventing HBV reactivation and its associated morbidity according to HBeAg status. Twenty-four adult HBsAg-positive NHL patients were taken 100 mg of lamivudine daily before the initiation of chemotherapy. The median duration of lamivudine therapy was 11.5 months (range: 1-54 months) and the median number of chemotherapy cycles was 6 (range: 1-16 cycles). The steroid containing chemotherapy regimens were used in 18 patients (75%), and the anti-CD20 monoclonal antibody containing chemotherapy regimen was used in 6 patients (25%). Four patients received autologous peripheral blood stem cell transplantation without resultant HBV reactivation. Hepatitis related to HBV reactivation was developed in 1 patient among 14 HBeAg-positive patients and no one among 10 HBeAg-negative. One patient developed HBV reactivation after lamivudine withdrawal, and 4 patients developed the YMDD (tyrosine-methionine-aspartate-aspartate) mutation during lamivudine therapy. There were no statistical differences in HBV reactivation rate during chemotherapy according to the HBeAg status. Our results demonstrate that lamivudine should be considered preemptively before the chemotherapy for all HBsAg-positive NHL patients to prevent HBV reactivation, regardless of pre-chemotherapy HBeAg status. Finally, compared with the chronic hepatitis B patients, similar rate of HBV reactivation after lamivudine withdrawal and development of YMDD mutation was observed in NHL patients.