The clinical Picture, course and outcomes of hepatitis A developing as a superinfection in children with chronic hepatitis B virus (HBV) infection, hospitalized in connection with acute viral hepatitis, were determined on the basis of the dynamic clinico-laboratory investigation and identification of viral hepatitides A, B and delta by the method of enzyme immunoassay. In all children hepatitis B virus surface antigen (HBsAg), i. e. the serological sign of HBV infection, and anti-HAV IgG, the serological sign of hepatitis A virus (HAV) infection, were present in the blood. 11 out of 12 children had never before been examined for diseases of the liver. Only in one child chronic HBsAg carriership had been detected 14 months before this hospitalization. Considering the data of epidemiological history and clinical observations, as well as the results of serological survey, these children were found to have hepatitis A superimposed on chronic HBV infection. As revealed in the present investigation, in cases of HAV superinfection observed simultaneously with chronic hepatitis B viral hepatitis A was manifested by typical clinico-laboratory symptoms.