Since 1990, the national strategy to eliminate hepatitis B virus (HBV) infection in Saudi Arabia has included universal administration of HBV vaccine to all infants. From 1990 to 1995 this vaccine was also routinely administered to children at school entry. The prevalence of hepatitis B surface antigen (HBsAg) among children before this programme was reported to be 6.7%. The objective of this study was to describe the trend in incidence of HBV infection over a decade of surveillance following the introduction of this programme. From January 1990 to December 1999 a total of 30,784 cases of HBV infection (positive for HBsAg) were reported. The total number of HBV infections among children <15 years of age was 4180 cases, with a prevalence of 0.05%. The total number of HBV infections among adults was 26,604 cases, with a prevalence of 0.22%. The prevalence varied by region, ranging from 0.03% to 0.72% with a mean prevalence of 0.15%. There was a clear decline in incidence among children whereas the incidence in adults slightly rose, perhaps owing to population growth estimated to be 3.3% annually. This study showed that the universal childhood HBV vaccination programme had an enormous positive impact on HBsAg seroprevalence among children in Saudi Arabia.