In a recent period of 64 months, fulminant hepatitis was diagnosed in 17 children at National Taiwan University Hospital. Eleven patients were younger than 12 months of age. Hepatitis A IgM antibody and delta-antibody were negative in all 17. Eleven (65%) patients had hepatitis B core IgM antibody, fulminant hepatitis B. Two to 5 months before onset of hepatitis. Five of the 11 children had received blood transfusions. Three of the five donors had hepatitis B e antibody (anti-HBe) and were hepatitis B virus DNA-negative hepatitis B surface antigen (HBsAg) carriers; another two were HBsAg negative, screened by a less sensitive reverse passive hemagglutination method. The mothers of all six infants younger than 6 months of age had HBsAg. HBe antigen and antibody were studied in five of these six mothers; all five had anti-HBe. We conclude that hepatitis B virus is the most important cause of fulminant hepatitis in children in Taiwan.