Hepatitis B reactivation is a well-known complication during or after chemotherapy in chronic hepatitis B (HBV) carriers. The current practice guidelines in Canada and the United States recommends patients receive antiviral prophylaxis prior to the onset of chemotherapy in chronic HBV carriers with lamivudine. We report a case of a 57-year-old man with follicular lymphoma on lamivudine prophylaxis and no clinical evidence of cirrhosis, and developed fatal HBV reactivation after the emergence of a YMDD mutant strain of HBV that confers lamivudine resistance. Fatal reactivation secondary to the development of lamivudine resistance has not, to date, been well- reported. Our experience indicates the need to carefully monitor patients for suspected drug- resistant HBV mutants with the addition of anti-viral agents effective against the YMDD mutational strain, when lamivudine resistance emerges.