We present a case of a clinical manifest hepatitis B virus infection and a potentially misleading HBV serological profile in an HIV-1 positive patient despite previous HBV vaccination. The patient presented with an acute hepatitis B and there was no indication of chronic HBV infection or the presence of a mutation in the 'a' determinant. Remarkably, simultaneously with high HBV surface antigen and HBV viral load, high anti-HBs antibodies were present. If, due to previous HBV vaccination only anti-HBs was tested in this patient, the result of the high anti-HBs antibodies could be very misleading and offering a false sense of security. Our findings contribute to the ongoing discussion on how to assess HBV specific immunological memory and determining the role of HBV booster vaccinations in immunocompromised individuals.