The benefit of lamivudine (LAM) in hepatitis B virus (HBV) infection is compromised by the progressively increasing emergence of drug-resistant mutant strains. Although the addition of adefovir dipivoxil (ADV) usually induces complete suppression of viral replication, primary non-response to ADV in LAM resistant patients has been reported in a variable percentage of cases. Here we report a case of a patient with HBV infection and hepatocellular carcinoma who started LAM therapy and subsequently developed virological breakthrough. The patient was given ADV, but HBV-DNA negativisation was not reached. However, HBV clearance was obtained when the patient was switched from ADV to tenofovir. Virological evaluations showed two well-known LAM-related mutations (rtL180M and rtM204I) in addition to reverse-transcriptase rtQ215H. This is the first case suggesting that this mutation may have an impact on viral replication. Finally, we also report that rtQ215H is responsive to tenofovir.