Alpha-interferon (IFN) has been used to treat hepatitis B virus carriers with chronic hepatitis Delta virus superinfection. Although the drug inhibits hepatitis Delta virus replication during administration, long-term clearance of the virus has not been obtained in most patients. The effectiveness of alpha-interferon on chronic HDV infection is therefore questionable. No data are available on acute infection. We report the case of a young, immunocompetent HBsAg carrier in whom hepatitis Delta virus superinfection occurred while he was receiving alpha-interferon in order to reduce high level HBV replication, and followed a peculiar course.