Hepatitis B, a disease entity currently affecting more than 350 million persons worldwide, is also a serious health problem in Taiwan. Liver cirrhosis and hepatoma, which are both closely correlated with hepatitis B, are among the 10 leading causes of death in Taiwan. A mass hepatitis B vaccination program, conducted by the government of Taiwan, was started in 1984. Prior to this vaccination program, a series of viral epidemiological surveys, transmission pattern studies, and pilot immunization trials proved the clinical, economic, and strategic benefits of mass immunization, thus providing the impetus for the implementation of this mass vaccination program. The success of this program has led to a decline in hepatitis B carrier rates among children in Taiwan from 10% to <1%. Furthermore, the mortality rate of fulminant hepatitis in infants and the annual incidence of childhood hepatoma have also decreased significantly in recent years. This is one of the most remarkable success stories in the field of public health.