Most chronic hepatitis B patients do not undergo a curative response to interferon-alpha or nucleoside/nucleotide-based regimens and require long-term therapy. Long-term safety, efficacy and resistance profiles of hepatitis B virus (HBV) drugs are therefore crucial issues for patient management. Adefovir dipivoxil is a nucleotide prodrug indicated for the treatment of patients with hepatitis B e antigen positive or hepatitis B e antigen negative chronic hepatitis B, lamivudine-resistant HBV infection, HBV infection pre- or post-liver transplantation, or HlV co-infection. Long-term data from clinical trials of up to 5 years duration of adefovir dipivoxil have recently become available and are reviewed here. These data demonstrate that adefovir dipivoxil therapy results in sustained efficacy and safety in the majority of patients after multiple years of treatment. The efficacy of adefovir dipivoxil in treating lamivudine-resistant HBV and the delayed emergence of adefovir resistance are key factors contributing to the durable response achieved in broad groups of chronic hepatitis B patients.