Chronic hepatitis B is often asymptomatic until it progresses to advanced stage. The natural course of disease includes flares and periods of decreased inflammatory activity. Immune decline status is proven risk factor for exacerbation of viral hepatitis. Anticancer chemotherapy in chronic HBsAg carriers is known to promote viral replication. Return of immunocompetence after withdrawal of immunosuppressant might result in liver damage. We describe case of a patient with chronic HBV infection who developed hepatitis flare subsequently to the cessation of anti-viral treatment and introduction of chemotherapy due to testicular seminoma. Patients with history of HBV infection who receive immunosuppressive treatment are at risk of HBV reactivation or exacerbation of hepatitis. During immunosuppressive treatment enhanced HBV replication and inhibition of CTL without evident liver injury is observed. Restoration of immune system after withdrawal of immunosuppressant allows recognizing increased expression of HBV antigens in hepatocytes. Intensive elimination of infected hepatocytes could occur resulting in liver tissue necrosis, active hepatitis and liver decompensation. It is recommended for HBV infected patients on immunosuppressive treatment to receive antiviral therapy, particularly with the lowest risk for the selection of mutations, regardless the stage of infection.