Only patients infected with hepatitis B virus (HBV) can contract hepatitis D virus (HDV) infection, either simultaneously (co-infection) or as a superinfection in those already infected with HBV. The routes of HDV transmission are contaminated needles or transfusion; sexual and vertical transmissions are relatively rare. Chronic hepatitis D is the most serious form of chronic viral hepatitis due to more rapid progression to decompensated cirrhosis and hepatocellular carcinoma (HCC). Liver cirrhosis may develop within five years and HCC within 10 years of dual infection. In the vast majority of cases, HDV replication suppresses HBV replication. Therefore, most patients are positive for HDV RNA in plasma while showing no or low levels of HBV DNA. At present, there is no routine screening for HDV in persons with chronic HBV infection in the Czech Republic. One of the reasons the absence of approved treatment op-tions, with the only possibility being administration of pegylated interferon alpha for 48 weeks or even longer. This approach does not provide long-term efficacy in most cases. Therapy with bulevirtide seems to be promising according to available data.