Twenty pediatric patients with primary hepatocellular carcinoma in Taiwan were tested for HBsAg, and all were found to be positive. The youngest case was 8 months of age, five cases occurred between 9 and 10 years of age, and 14 cases occurred between 11 and 16 years of age. The serum alpha-fetoprotein was elevated in all 20 primary hepatocellular carcinoma patients, and the average survival of these cases after diagnosis was 4.7 months. Seventy per cent of the mothers of the pediatric primary hepatocellular carcinoma cases and 52.9% of their siblings who were tested also were positive for HBsAg. In addition, two families had clustering of primary hepatocellular carcinoma cases. The occurrence of primary hepatoceullar carcinoma in the pediatric age group suggests the need for close follow-up of young HBsAg-positive carriers. Also, prevention of perinatal transmission of hepatitis B virus by immunoprophylaxis will significantly decrease both the hepatitis B virus carrier rate and the incidence of primary hepatocellular carcinoma in the asian population.