AbstractThe prevalence of intrahepatic delta antigen and/or anti‐delta antibody was retrospectively investigated in 102 children with chronic HBsAg‐positive hepatitis who were seen consecutively in three medical institutions between 1974 and 1982. Delta infection markers were found in 13 patients (12.7%) who exhibited high serum titers of anti‐delta antibody; intrahepatic delta antigen was detected in ten. Eleven of the 13 children had severe progressive liver disease associated in all but one with absence of hepatitis B virus replication as evaluated by analysis of serum hepatitis B virus DNA. The factors which seem to increase the risk of delta infection in children who are hepatitis B virus carriers are geographic origin, a history of exposure to blood derivatives and age. A further 37 of 102 children had chronic active hepatitis (20 patients) or cirrhosis (17 patients) without evidence of delta infection. These results indicate that delta infection occurs in children with chronic hepatitis. This possibility should be considered in investigation of children with HBsAg‐positive chronic liver disease. Although the delta agent is an important cause of progressive liver disease in children who are chronic HBsAg carriers, severe liver injury and especially cirrhosis can occur without evidence of delta in