Coinfection of hepatitis B virus (HBV) and HIV is common due to overlapping routes of transmission accompanied by an increased risk for liver-related mortality. We report the case of a chronically infected hepatitis Be antigen positive patient, coinfected with HIV (CD4+ T-cell count > 500 cells/microl), with histological evidence of advanced liver disease. The patient developed anti-HBs (antibody to hepatitis B surface antigen [HBsAg]) seroconversion, a strong reduction of intrahepatic covalently closed circular DNA and a marked improvement of liver histology after 24 weeks of HBV-targeted combination therapy with adefovir dipivoxil and pegylated interferon-alpha2b followed by another 12 weeks of adefovir dipivoxil monotherapy. Antiviral therapy was stopped after the development of stable anti-HBs titres, and anti-HBs titres remained stable for additional 9 months post-treatment. A continuous decline of anti-HBs was observed during the next 6 months until anti-HBs disappeared despite a stable HIV infection. A triple course of therapeutic vaccination failed to re-establish anti-HBs antibodies, but reappearance of HBV DNA and HBsAg was detected. By enzyme-linked immunosorbent spot analyses, HBV-directed T-cell responses clearly increased during antiviral combination therapy followed by a reduction to pre-treatment levels in association with disappearance of anti-HBs antibodies despite therapeutic vaccination. The presented case highlights the volatile nature of chronic HBV infection even after a prolonged disease-free period in the setting of an underlying HIV coinfection in a patient with a stable and relatively high CD4+ T-cell count but nevertheless impaired immune system and calls for further investigation of probably temporary immunomodulatory effects of interferon-alpha and/or nucleoside analogues in immunocompromised patients.