The use of rituximab has been associated with increased risk of hepatitis B virus (HBV) reactivation in patients who are hepatitis B surface antigen (HBsAg) negative and antihepatitis B core antibody (anti-HBc) positive. We aim to determine the rate of HBV reactivation in this group of patients who received rituximab-containing combination chemotherapy without concomitant antiviral prophylaxis and to identify potential risk factors for reactivation. Sixty-two HBsAg negative/anti-HBc positive patients with B-cell lymphoma treated with rituximab-based immunochemotherapy from 2006 to 2009 were included. None of the patients received concomitant antiviral prophylaxis. In this cohort, 48 (77%) patients received rituximab with cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP), eight (13%) received rituximab with cyclophosphamide, vincristine and prednisolone, and six (10%) received other chemotherapy regimens. Two patients suffered HBV reactivation; both were above 70 years of age, received R-CHOP chemotherapy and were negative for antihepatitis B surface antibody (anti-HBs) at baseline. One of the two patients reactivated shortly after completion of R-CHOP chemotherapy while the other reactivated during rituximab maintenance treatment. Thus, the overall reactivation rate in this cohort of patients is 3% (2/62), 4% (2/48), and 25% (1/4) in patients who received R-CHOP chemotherapy and who received rituximab maintenance, respectively. The rate of HBV reactivation is low in patients who are HBsAg negative/anti-HBc positive receiving rituximab-based combination chemotherapy without concomitant antiviral prophylaxis. However, elderly patients, particularly those without anti-HBs, seemed particularly at risk.