Universal vaccination against hepatitis B virus (HBV) was introduced for all newborns in Bulgaria in August 1991, after a three-year selective immunization of babies born to HBsAg-positive mothers. In 1992, a coverage level of 71.3% was achieved. Since 1989, hepatitis B morbidity among infants shows a continuing downward trend with the lowest annual incidence rate, 0.3 cases per 100,000, in 1992. This represents an 82% decrease compared to the preimmunization period. As strong epidemiological evidence exists that an early age of infection substantially increases the overall burden of chronic HBV infection, future expansion of vaccination coverage to include all children up to 6 years of age was considered an appropriate alternative to the existing policies.