Hepatitis D (also known as hepatitis delta) is a liver disease caused by a small spherical enveloped RNA virus known as the hepatitis D virus (HDV). However, it is a defective virus and to cause disease it requires the help of HBV. Hence, both HDV and HBV need to be present together to cause hepatitis D disease.

HDV is found only in patients who are infected with the HBV. HDV may worsen the condition of liver disease patients who have either acute (recent) or chronic (long-term) hepatitis B. HDV may lead to development of symptoms in patients with HBV who were till now asymptomatic.

Treatment of infection with HDV consists primarily of supportive measures. No pharmacologic treatment for hepatitis D has been approved. Few studies have found that treatment with peg-interferon injections for 1 year may lead to clearance of HDV in approximately 25% of patients.