More than 30 years after Mario Rizzetto and colleagues described a new antigen in livers of HBsAg-positive patients called the “delta antigen”, a re-emerging interest in hepatitis delta is currently observed. The state-of-the art on basic and clinical research on hepatitis delta was presented during a monothematic conference organized by the European Association for the Study of the Liver (EASL) in September 2010. Hepatitis delta is caused by infection with the hepatitis D virus (HDV) which requires presence of HBsAg for complete replication and transmission. Recent data confirmed the severe long-term course of HDV infection with high rates of hepatic decompensation while controversial data on the risk for the development of hepatocellular carcinoma were reported. Pegylated interferon alpha can lead to sustained HDV RNA elimination in about one quarter of patients while HBV polymerase inhibitors are ineffective against HDV. Novel treatment options include prenylation inhibitors and HBV entry inhibitors which are currently in early clinical development.