Hepatitis B virus (HBV) is endemic in the Kingdom of Saudi Arabia. To prevent the chronic carriage of HBV in Saudi children, hepatitis B vaccine was added as the seventh immunogen in the expanded program on immunization (EPI). In the first year, the coverage of the first dose and third dose of HB vaccine was 90% and 73%, respectively. In a survey of 637 children, 603 (95%) were positive for antibody to hepatitis surface antigen (anti-HBs) without concomintant antibody to hepatitis B core antigen (anti-HBc) or hepatitis B surface antigen (HBsAg). A total of 592 (93%) with anti-HBs titer of > 10 IU/L were considered as responders to the vaccine. The majority (60%) of these responders had titers > 100 IU/L. Only one (0.3%) non-responder was positive for anti-HBc alone. Using historical control, the protective efficacy was estimated as 99%. Neither the gender of the recipient, schedule of the vaccination, nor the sourve of vaccine influenced the response to the vaccine. The successful integration of the HB vaccine into the EPI was due to the effectiveness of the EPI and the efficient primary health care system in Saudi Arabia.