Hepatitis B is an inflammation of the liver caused by a virus. The virus spreads from person to person through contact with infected body fluids. For example, the virus can be spread through sexual intercourse or contaminated needles or blood or from mother to baby at birth. Most people with hepatitis B recover within a few months, but some develop chronic inflammation, permanent scarring (cirrhosis), or liver cancer. Vaccines that contain small amounts of dead or altered virus can boost the body's normal defense (immune) system and help prevent hepatitis B and related complications. Taiwan has had very high rates of hepatitis B. In the mid-1980s, Taiwan began a program of universal hepatitis B vaccination for newborns, school children, teenagers, and young adults. This study describes the success of that program.